Ruler Measuring Game: Ruler Ready
Ruler Ready is a free measuring game that teaches children how to use a ruler properly. They slide the ruler until its 0 mark lines up with the start of a pencil, leaf, caterpillar or key, then read the length. Levels move from whole centimetres to half centimetres, millimetres, and writing lengths in both cm and mm, with a level for estimating before measuring.
Ruler Ready
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- Ages
- 6–10
- School years
- Grade 1–Grade 4
- Skills
- Using a ruler correctly: starting at 0, not at 1 or the edge of the ruler, Measuring length in whole centimetres and half centimetres, Measuring when an object does not start at 0 (end − start)
- Time
- 5–10 minutes a game
- Cost
- Free, no sign-up
- Updated
How to play Ruler Ready
- Choose a level and press Play. Level 1 is whole cm, Level 2 has objects that do not start at 0, Level 3 is half cm, Level 4 is mm, Level 5 is cm and mm, and Level 6 is estimate first, then measure.
- Line up the ruler: drag it left or right, or use the ◀ and ▶ buttons (arrow keys work too), until the 0 mark is exactly at the start of the object. The zoom window shows the start up close. Press Check, or let go when it is lined up.
- Read the length: look straight down from the end of the object to the ruler and type the number on the number pad. Use the ½ key for half centimetres and the point key for lengths like 7.4 cm.
- If you line up the 1 instead of the 0, or the end of the ruler instead of the 0 mark, the game tells you. Wrong readings get a hint that explains the mistake.
What your child learns
- Using a ruler correctly: starting at 0, not at 1 or the edge of the ruler
- Measuring length in whole centimetres and half centimetres
- Measuring when an object does not start at 0 (end − start)
- Reading millimetres on a ruler
- Writing lengths in cm and mm (7.4 cm = 74 mm)
- Estimating length before measuring
About Ruler Ready
Using a ruler looks easy, but many children make the same mistakes: they line up the 1 instead of the 0, line up the edge of the ruler (most rulers have a small gap before 0), or count the marks instead of the spaces between them. Ruler Ready lets children practise lining up a ruler again and again, and gives a clear message when they make one of these mistakes. Measuring with a ruler in cm is taught in Grade 1 and Grade 2, and the rulers and objects in the game are drawn to scale with each other, so a 6 cm key really is twice as long as a 3 cm one.
Later levels build on that. In Level 2 the object starts partway along the ruler, so children subtract the start from the end, the way they measure part of a line in Grade 3. Levels 3, 4 and 5 move to half centimetres and millimetres, with a zoom window that shows the small marks clearly, and practise writing the same length two ways: 7 cm and 4 mm is 7.4 cm, which is 74 mm. Level 6 asks for an estimate first, using a 1 cm cube for comparison, then checks it by measuring. There is no timer, and every mistake gets a hint.
Which level should my child play?
| School year | Suggested level |
|---|---|
| Grade 1 | Level 1: line up 0 and measure in whole cm |
| Grade 2 | Level 2: objects that do not start at 0, then Level 3: half cm |
| Grade 3 | Level 3, then Level 4: measuring in mm |
| Grade 4 | Level 5: cm and mm, such as 7.4 cm = 74 mm, and Level 6: estimate first, then measure |
Move up a level after getting three stars two or three times in a row.
🏆 Leaderboard
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Frequently asked questions
How do you teach a child to use a ruler?
Show them the 0 mark first, and explain that measuring always starts at 0, not at the edge of the ruler or at 1. Line up 0 with one end of the object, then look straight down from the other end and read the number. Ruler Ready practises exactly these steps.
Why is starting at 1 a mistake?
The numbers on a ruler mark the end of each centimetre. If you start at 1, the first centimetre is already used up, so the answer is 1 cm too long. If you must start somewhere else, subtract the start: an object from 3 to 9 is 9 − 3 = 6 cm long.
How many mm are in a cm?
There are 10 millimetres in 1 centimetre. A length of 7 cm and 4 mm can be written as 7.4 cm or as 74 mm. Level 5 practises changing between them.
Does the game use inches?
The levels are in centimetres and millimetres. On our US site there is also an inches level that measures to the nearest half inch and quarter inch.
Which level should my child start on?
Start on Level 1 in Grade 1. Children in Grade 2 can try Levels 2 and 3, Level 4 suits Grade 3, and Levels 5 and 6 are good for Grade 4.
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