Comparing Length, Weight and Capacity

A bottle can be tall, light to carry, and able to hold plenty of water. Help your child choose one question before checking it. “Which is bigger?” needs a little more detail.

Give each question a name

Length is how long something is from end to end. Height is how tall it stands, from bottom to top. Weight is how heavy it is. Capacity is how much fits inside a container when it is full.

Set out a bottle and a lunch box. Point from the bottom to the top as you ask, “Which is taller?” Hold them to ask, “Which is heavier?” Looking at their tops will answer the first question. It will not answer the second.

Full and empty tell how much is inside right now. An empty bottle still has room to hold water.

Make “big” more useful

When your child says, “This box is bigger,” ask, “Bigger how?” They might point to its tall sides or lift it. Help them finish the thought: “This box is taller than that box.” Naming both objects makes the comparison clear.

Try a long ribbon and a shoe. The ribbon can be longer while the shoe is heavier. Check the length by laying them out. Check the weight by holding them. One result does not settle every question about the pair.

Turn it and talk

Stand a pencil on its end while you hold it steady. Say, “We can talk about how tall it stands.” Lay it down and say, “Now we can talk about how long it is.” Turning it did not change the distance from one end to the other.

Comparisons also depend on the partner. A pencil may be longer than a crayon and shorter than a broom. Ask your child to name the partner each time: “The pencil is shorter than the broom.”

If your child sorts objects by color during a length activity, point to the ends. Ask, “Which reaches farther?” Color helps find the object you mean; the ends help compare its length.

A spoon can seem longer just because someone pushed it forward. Let your child move objects into place before deciding. A shared starting line makes the far ends useful.

Compare two lengths

Use a fork and a spoon. Lay them beside each other on a table. Put both handle ends at the table edge. Keep each object pointing straight away from that edge.

Now trace along each one with a finger. In this example, the fork reaches past the spoon. Say, “The fork is longer than the spoon.” Invite the reverse sentence: “The spoon is shorter than the fork.” Both sentences describe the same pair.

Point to the part of the fork that sticks out beyond the spoon. This shows the difference. You can say “a little longer” or “much longer” without counting yet.

Move it without changing it

Slide the spoon forward until its tip passes the fork. Ask your child to check the starting ends. Bring both handles back to the edge and compare again. The spoon moved, but its length stayed the same.

Bendy objects need another check. Smooth a curled ribbon into a straight line before laying it beside a belt. Keep it straight without pulling it longer. Rolling a rope into a coil does not shorten the rope itself. Cutting a piece off does.

Compare heights from the bottom

Stand two stuffed animals upright on the same flat surface. First look at their bottoms. Then look across their tops. The one reaching higher is taller.

A toy on a box has a head start. Put it on the same surface as the other toy before comparing. For people, use the same floor, feet flat, with both barefoot or both wearing shoes. Standing on tiptoe changes the starting setup.

Notice an equal match

Sometimes both ends match. Line up two straws at one end and look at the other. If those ends match too, say, “They are the same length,” or “This straw is as long as that one.” Keep equal pairs in your activities so your child has a reason to use those words.

Three objects give your child a new job: finding a place for each one. Choose lengths that are easy to tell apart at first. Keep all three starting ends lined up while you work.

Build a row that goes one way

Set out red, blue and yellow crayons. In this example, the blue crayon reaches farthest. The yellow reaches the least far, and red ends between them.

1. Put yellow at the start of a shortest-to-longest row.
2. Put blue at the other end.
3. Place red between them.

Read the order together: “Yellow, red, blue.” Ask, “Which is longest? Which is shortest?” Then point to red: “It is longer than yellow and shorter than blue.” That explains its middle place.

With two things, use “longer” and “shorter.” In a group, “longest” names the one that reaches farthest. For standing objects, use “taller” and “tallest.”

Read the row backward

You can also order from longest to shortest: blue, red, yellow. Ask which end should come first before your child starts. A row that goes long, short, then longer changes direction halfway through. Return to the shared edge and find the middle again.

Try the same activity with three stuffed animals standing on the same floor. Your child can find the tallest, the shortest and the one between them by looking across their tops.

Change the group

Take the longest crayon into a new group with a pencil and a ruler, both longer than that crayon. Now the crayon is shortest. Its length stayed the same; its partners changed. Ask, “Shortest out of which things?” as you point to the new group.

When things cannot sit together, compare pairs. If a scarf is longer than a belt, and the belt is longer than a shoelace, the scarf is longest of the three. Lay out the pairs again if your child wants to check.

Leave room for a tie

If two straws match and a pencil is longer, keep the straws together at the short end. Say, “These two are the same length. The pencil is longer than both.” There does not have to be a different length for every place.

A large object can be easy to lift, while a small one feels heavy. Let your child make a guess, then feel the objects. Surprises give you something useful to talk about.

Compare with two hands

Give your child a can of beans and a box of tissues. Ask which they think will be heavier. Then have them hold one in each hand, palms up. The hand holding the can is pulled down more. The can is heavier, even though the tissue box looks bigger.

Say both comparisons: “The can is heavier than the tissue box.” “The tissue box is lighter than the can.” Weight means how heavy something is, or how hard it pulls down when held.

Try lifting a backpack before and after packing it. Ask, “What made it heavier?” Your child can point to the things added inside. Two matching bottles can also weigh differently when one is full and one is empty. Their outside size does not show everything about their weight.

A new shape, the same dough

Roll a ball of play dough into a long snake. Keep all the dough together. Ask whether its weight changed. It did not: no dough was added or taken away. A balance scale lets your child check the ball and snake against the same load before and after reshaping.

If some dough breaks off and is left behind, you are now weighing less dough. Put it back before checking whether shape alone changed the weight.

Order three by feeling pairs

Pick three objects with clearly different weights. Compare two and keep track of the heavier one. Compare that one with the third object to find the heaviest. Then compare the two remaining objects to find the lightest. The last object belongs in the middle.

Help your child describe the row: “lightest, heavier, heaviest,” or name each object from lightest to heaviest. Use “as heavy as” when two feel alike, and check with a scale if the difference is hard to feel.

Hands are useful for a clear difference. Close weights are harder to judge. When your child says, “I cannot tell,” bring out a balance scale and let the pans show the difference.

A balance scale makes a small weight difference easier to see. Its two pans hang on opposite sides of a middle point. Start with the empty pans level, then let your child add the objects gently.

Follow the lower pan

Wait until the scale stops moving. The lower pan holds the heavier load. The higher pan holds the lighter load. If the pans settle level, both loads weigh the same.

Put a potato in one pan and a carrot in the other. In this example, the potato pan goes down. Say, “The potato is heavier than the carrot.” You can also say, “The carrot is lighter than the potato.”

Children sometimes choose the higher pan because “higher” feels like “more.” With empty pans, press one gently downward. Point to the pan you pushed. Then release it before weighing. This connects the downward pull with the heavier side.

Use pairs to order three

Try a book, cup and shoe. Suppose the book pan goes down against the cup. The book is heavier. Next compare the book and shoe. The shoe pan goes down, so the shoe is heavier than the book.

You now have the order: shoe, book, cup, from heaviest to lightest. If the book had been heavier than both other objects, you would still need to compare shoe with cup. Knowing the heaviest does not settle which of the other two is lightest.

Make the pans level

Put a toy car in one pan. Add matching blocks to the other, one at a time. If the pans settle level, those blocks together weigh the same as the car.

Sometimes 5 blocks leave the car pan lower, while 6 blocks pull their own pan lower. The car weighs more than 5 blocks but less than 6. To make a level match, return to 5 blocks and add small bits of play dough to that pan. Stop when the pans settle level.

Adding to the lighter side or taking from the heavier side brings the loads closer. Read the scale again after every change.

Set up a homemade balance fairly

A coat hanger can hold two matching cups or bags. Hang them at equal distances from the middle and hold the hook. Check the empty containers hang level. Different containers or unequal hanging distances can tip the hanger before any objects are added.

“How much water is in it?” and “How much can it hold?” are different questions. Put an empty jug beside a full cup and talk about both. The empty jug has no water now, but it still has room inside.

Name how full it is

A full container holds as much as it can, right to the top. An empty one has nothing inside. Between those, use “nearly empty,” “half full” and “nearly full.”

Half full means half the amount the container can hold. In a glass with straight, upright sides, water halfway up is about half full. A container that gets wider toward the top needs a different check; halfway up does not always mean half its capacity.

Set out matching clear glasses with different amounts of water. Ask your child to describe each one. They can put the glasses in order from nearly empty to full, watching where the water reaches.

Separate now from full

Capacity is the amount a container holds when full. A large jug with a little water may have less water now than a full cup. The jug can still hold more when both are filled.

Point inside as you ask, “What is in here now?” Then point to the top: “How much could fit?” Use the same questions with a toy box containing just one block. Empty space is part of the room available to fill.

Check a change of shape

Pour all the water from a short, wide glass into a tall, thin glass. Do not add water or spill any. The water reaches higher in the narrow glass, but the amount stayed the same. Pour it back so your child can see the original level return.

Water height lets you compare amounts directly in matching containers standing on the same surface. Different shapes can put the same amount at different heights. Pour into matching containers when you need to compare those amounts by eye.

You can practice these words while watering plants or washing dishes. Ask, “Is it nearly full?” as your child pours. Stay with your child throughout water play, even with shallow water.

A tall container does not always have the most room inside. Filling and pouring lets your child check. Use a tray or sink to catch overflow, and keep track of which container starts full.

Set up a fair pour

Fill the first container right to the top. Leave the second empty. Pour carefully from the full one into the empty one, watching when the water reaches the top.

A half-filled first container would test just that smaller amount of water. Fill it completely when you want to compare what the containers can hold. If water spills on the way across, empty the containers and repeat the test.

Watch a mug and bowl

Fill a mug and pour into an empty small bowl. In this example, the bowl fills and overflows before the mug is empty. The water that remains in the mug shows that the mug holds more. Say, “The bowl holds less than the mug.”

Do not decide by height alone. A short, wide pot may hold more than a tall, thin vase. Let your child guess, then test the pair by pouring.

Order three containers

Use a jug, mug and egg cup. Suppose the full jug fills the mug with water left over. The jug holds more than the mug. Then the full mug fills the egg cup with water left over. The mug holds more than the egg cup.

From most to least, the order is jug, mug, egg cup. If you only knew that the jug held more than both others, you would need one more test between the smaller two.

Use matching jars for a clear view

You can fill two different containers, then pour each into its own matching clear jar. Choose jars large enough to hold all the water. Stand them on the same surface. The higher water level now shows the larger capacity because the receiving jars match.

To make amounts equal in two matching glasses, pour a little from the fuller one into the emptier one. Stop when the water levels match.

You cannot easily put a sofa beside a table to compare their lengths. A string can carry one length to the other place. A paper strip or ribbon works too, as long as its marked length stays the same.

Match the first object

Lay a string straight along the table from one end to the other. Start exactly at the near edge. At the far edge, pinch the string or mark it. You can cut it there with your help.

Now the marked part is as long as the table. Keep that length while carrying it to the sofa. If you let go of an unmarked pinch, match the table again before checking the sofa.

Read it against the second object

Line up the string's starting end with one end of the sofa. Hold it straight along the sofa's length.

• If the string stops before the sofa ends, the sofa is longer.
• If the string goes past the sofa's end, the table is longer.
• If the string fits exactly, both lengths are the same.

In the table-and-sofa example, the string stops short of the sofa's far end. Say, “The table is shorter than the sofa.” The string matches the table, so its shortfall tells you about the table too.

Keep the match honest

A sagging string takes a longer path between the table's ends. That gives you too much string. A curled string at the sofa uses up some of the marked length sideways. Hold it straight for both matches, without stretching it.

Check the starting edge each time. Beginning a little inside an object leaves out part of its length. Let your child point to both ends before making the match.

Try a body landmark

Your child's body can help compare heights too. Standing on the same floor, the chair may reach their tummy and the table their chest. The table reaches higher on the same child, so it is taller. Keep the child standing upright for both checks.

Two short paper strips can also make one longer strip. Put their ends together, with no gap or overlap, then compare the combined length with a long strip. This prepares your child to repeat one small unit along a length.

Measuring gives your child a number as well as a comparison. The small object repeated along a length is the unit. Start with objects your child can line up and count easily.

Measure a book with paper clips

Collect matching paper clips. Put the first at the book's bottom edge and lay more end to end toward its top. Each clip touches the next. Keep every clip pointing in the same direction along a straight line.

In this example, 7 clips reach exactly from one edge to the other. Touch each once as you count. Say the number with the unit: “The book is 7 paper clips long.” The word “clips” tells someone what you counted.

A fair line follows four rules:

1. Start exactly at one end.
2. Keep the line straight.
3. Leave no gaps or overlaps.
4. Use units of the same size.

See what gaps and overlaps do

Spread those clips apart along the same book. The empty spaces cover some of the length, so fewer clips seem to fit. The count is too small. Push the clips back until their ends touch.

Now overlap the clips. More clips fit along the book because part of each clip covers a place already covered. That makes the count too big. Let your child fix one overlap at a time and count again.

A mixture of big and small blocks gives no single block size to repeat. Gather a matching set before measuring, and keep the blocks facing the same way.

Say when the end falls between units

Often the book ends between two clip ends. If 7 clips fit and part of an eighth is needed, say, “A bit more than 7 paper clips long.” If a seventh clip sticks out just a little, “about 7 paper clips long” is useful. Do not call an in-between fit exact.

Choose a useful unit

Cubes work well beside a shoe. For height, build a cube tower upward beside a toy from the same surface. Count the cubes reaching its top.

For a rug, your child can place one foot heel to toe after the other, keeping each heel against the previous toes. Say, “The rug is 9 of my feet long.” Hand spans can measure a table. A tiny unit along a whole room may give too many to count; a large unit across a small object may not fit even once.

A unit can measure more than length. Cubes can show how heavy an object is. Repeated scoops can show how much a container holds. In both activities, each counted unit must match the others.

Weigh with matching cubes

Check a balance scale is level when empty. Put an apple in one pan. Add identical linking cubes to the other pan, one at a time. Wait for stillness after each cube.

Suppose the apple pan is still lower with 8 cubes. Add a ninth. The pans settle level. Your child can say, “The apple weighs 9 cubes.” All 9 cubes together balance the apple; one cube is the unit.

Sometimes the apple pan is lower with 8 cubes, but the cube pan is lower with 9. Then its weight is between the two counts: “More than 8 cubes but less than 9.” You can also describe it as “about 9 cubes.” An exact level match is different from a close count.

Use identical cubes of one kind for the weighing. Matching outside sizes alone would not make wooden blocks and hollow plastic blocks equal weights.

Fill with repeated scoops

Start with an empty jug and one small scoop. Fill the scoop to the top, pour it into the jug, and count aloud. Repeat with the same scoop, filled the same way each time.

If 6 whole scoops fill the jug exactly, say, “The jug holds 6 scoops.” If 5 fit and only part of the sixth fits, say, “More than 5 scoops but less than 6.” Start over after a spill so the count describes what actually reaches the jug.

For dry rice or sand, level each scoop at the top. A heaped scoop contains more than a level scoop. Switching between heaped and level scoops changes what “one scoop” means halfway through.

Fill a box with solid units

You can count how many matching blocks fit inside a box. Pack them neatly in rows. Tipping them in loosely leaves spaces, so fewer may fit. Keep the same blocks and packing method when comparing two boxes.

A number becomes useful when you know its unit. Help your child keep the number and unit together in a drawing or spoken answer. Then you can compare results without measuring everything again.

Compare like with like

A spoon measures 5 paper clips and a crayon measures 3 of the same clips. The spoon is longer because 5 matching units cover more length than 3. To find the difference, start at 3 and count on: “4, 5.” That is 2 more clips.

Lay the objects at the same starting edge. The extra part of the spoon is about 2 clips long. This connects the counted difference with a part your child can point to.

Weight works the same way. An apple balances 9 identical cubes; an orange balances 7 of those cubes. Count on from 7: “8, 9.” The apple is 2 cubes heavier.

Order three counts

Suppose a pot holds 9 scoops, a jug 6 and a bottle 4. Every scoop is the same size and filled the same way. From most to least, the order is pot, jug, bottle. Ask which holds the most, which holds the least and which belongs in the middle.

Draw each container and write its count beside it. If writing is still hard, your child can make a cube tower for each count using identical cubes. Taller towers show larger counts. Keep the object labels beside the towers so you know what each count describes.

Change the unit, watch the number

Your child measures a table in 10 of their hand spans. Dad measures it in 6 of his larger hand spans. The table did not change. Bigger units cover more at each repeat, so fewer are needed.

The same pencil can measure 6 paper clips or 9 smaller cubes. The bigger number does not show a longer pencil. It shows that the cubes are smaller units. For a fair comparison between different objects, measure both with the same unit.

Guess, then find out

Before measuring a shoe, ask, “How many cubes do you think will fit along it?” Suppose your child guesses 5 and measures 7. Say, “It took 2 more cubes than your guess.” Keep the guess and the measured result in separate spots on the page. A close guess helps build a feel for size; the fair measurement gives the count.