Skills / Ages 8 to 11 / Math
Measure with a ruler
Laying a ruler along something with the zero mark at one end, reading the mark at the other end to the nearest centimeter, and writing the unit after the number.
Why it matters
Lengths show up in almost every kitchen test: how tall a bean plant grew, how far a marble rolled. A child who lines up the zero, reads the right mark and writes centimeters after the number gives a result anybody could check with their own ruler.
What it looks like when your child can do it
- Your child finds the zero mark first, which is often a little way in from the end of the ruler, and lines it up with the edge of the thing.
- A spoon ends a little past the 17 mark, not yet halfway to 18, and your child writes 17 cm.
- Your child writes cm after every number without being reminded.
How to teach it at the kitchen table
- 01
Find the zero before anything else
On many rulers the zero is a line a little way in from the end, not the end itself. Show your child where it is and line that mark up with one end of the object.
- 02
Use the centimeter edge
Most rulers have inches on one edge and centimeters on the other. The book measures in centimeters, so find the edge marked cm and use it every time.
- 03
Read the mark at the far end
Keep the ruler flat and straight along the object. Look straight down at the far end and read the numbered mark it reaches.
- 04
Pick the nearest centimeter
If the end falls between two numbers, choose the one it is closer to. A pencil that ends a little past 12, not yet halfway to 13, is 12 cm.
- 05
Write the number with its unit
12 by itself is half an answer. 12 cm is the whole answer. Ask for the unit every time until your child writes it without thinking.
You will need: A ruler with centimeters · Crayons, spoons and pencils to measure · Paper and a pencil
Try it together
Try 1
Hand your child a crayon or a pencil and ask how long it is in centimeters.
Listen for Measure it yourself first. Watch that the zero mark, not the end of the ruler, sits at one end of the crayon.
Try 2
Lay a crayon so it starts at the 1 cm mark and ends at the 9 cm mark. Ask how long it is.
Listen for 8 cm, because 9 minus 1 is 8. This is the stretch question. Reading the far end alone gives 9, which is wrong.
Try 3
Describe a spoon that starts at zero and ends a little past the 17 mark, not yet halfway to 18. Ask what to write.
Listen for 17 cm. The nearest mark is 17, and the unit goes on the end.
Try 4
Ask your child to draw a line exactly 10 cm long with the ruler.
Listen for A line from the zero mark to the 10 mark. Check it with the ruler yourself.
Watch for
- Starting from the end of the ruler instead of the zero mark, which makes every measurement come out a little short.
- Reading the inch edge by mistake. The numbers come out much smaller there, so a 15 cm spoon reads as about 6.
If it is not there yet
- Measure things that end right on a numbered mark first, like a strip of paper you cut to 10 cm ahead of time.
- Put a small sticker on the zero mark so your child's eye goes there first.
A few days of this is normal, and it is time well spent. The lesson will still be there, and it will go faster.
Where this skill comes up
How Scientists Actually Find Out · Lesson 15
The Thing You Measure
Needs it because the outcome on the sheet is a length, and it has to be read off a ruler to the nearest centimeter.