Measuring length (age 7+)
Measure the length of an object by selecting and using appropriate tools such as rulers, yardsticks, metre sticks, and measuring tapes
What a learner can do afterwards
- Choose the most appropriate tool for measuring a given object
- Align the zero mark of a ruler with the end of the object and read the measurement
- Measure lengths in inches, feet, centimetres, and metres using the correct tool
1 · Read
You measured with equal units laid end to end. Rulers mark equal length units. A short ruler suits small straight objects. The shortest tool that covers an object can be easier to handle. A flexible tape follows curved edges.
Length units include centimetres (cm), metres (m), inches and feet. A metre stick is 1 metre long. A yardstick is 3 feet long. Some tools show two scales. Choose the scale with the unit you need. Put one end at zero, hold the tool still and read the other end. Write the number and unit. From 0 to 4 on an inch scale means 4 inches.
Ana has fabric about 80 cm long. Her ruler reaches 30 cm and her tape reaches 150 cm. The tape covers the fabric in one placement. She holds it straight along the fabric, with zero at one edge. The other edge reads 80 cm. Check a tool's reach before choosing it. A shorter tool needs repeated placements.
Use the zero mark, which may be inside the ruler's edge. Length counts spaces between marks. From 0 to 5 there are 5 spaces but 6 marks. If you start away from zero, subtract the start reading from the end reading. A strip from 4 cm to 11 cm is 11 - 4 = 7 cm long.
A short tool can measure a longer length in parts. Mark each placement's end. Put zero at that mark for the next part, with no gaps or overlaps. Add all parts in the same unit. Three full 1-metre placements measure 3 metres. Parts of 10 cm, 10 cm and 4 cm measure 24 cm.
Keep a tape straight and flat when measuring a straight length. A drooping tape takes a longer path between the ends. For a curved edge, follow the curve without stretching the tape. Measuring straight across gives a different length. Keep both ends in place while you read.
Check how much length each space on a scale represents. A tape's numbered marks might count 2 feet at a time: 0, 2, 4, 6. Each space between these marks covers 2 feet. A rug from 0 to 6 is 6 feet long, not 3 feet. Read the numbers and write feet as the unit.
Pick a tool long enough for the job, line up its zero mark, and read the length in the right unit.
Lesson, questions and flashcards written for this dataset.
Questions, readings and flashcards written for this dataset. Referenced videos are by Khan Academy.
More to read
Keep the number with its unit
A ruler may have more than one scale. Before measuring, find the unit you need. cm means centimetres. An inch scale counts inches.
Place the object's starting end at zero. Keep the object and tool still while you read the other end. Write the number beside the unit from that scale. Switching scales while recording changes the meaning of the number.
Check the tool's reach
Look at how far a measuring tool reaches. A tool at least as long as the object can cover it in one placement. A shorter tool needs several placements.
A short ruler is handy on a desk. A long tape reduces the moves needed across a room. A flexible tape can follow a curved edge. Hold it straight for a straight length, or follow the curve when measuring along an edge.
Marks and spaces
Ruler marks show where units begin and end. Marks at 0, 1, 2 and 3 make three spaces from zero to three. Counting all four marks would not give the length.
Starting at zero lets you read the length directly at the other end. If your starting reading is not zero, subtract it from the ending reading. The difference counts the spaces covered by the object.
Move a ruler carefully
Measure the first part of a long object. Mark where the ruler ends, then move its zero to that mark. Repeat until you reach the object's far end.
Keep the ruler along the measured edge. Do not leave a gap or count an overlapping part twice. Record every part in the same unit. Add the parts, including the last part if it is shorter than the ruler.
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