How to read a tape measure in millimetres, centimetres and inches

1. Identify the scale and starting point

Check the blade itself before counting lines. Stanley's UK TYLON 0-30-696 has metric and imperial scales, while its Grip STHT0-33561 is metric. A familiar case shape does not tell you which scale you have. Work along one scale and keep the tape aligned with the dimension you intend to record.

Place the hook against the intended starting edge, using the outside or inside measuring position appropriate to the job. Read at the endpoint, looking straight at the mark. If you deliberately start at a numbered mark instead of zero, subtract that starting reading; do not record the endpoint alone.

2. Count millimetres after the whole centimetres

There are 10 millimetres in one centimetre. On a metric tape divided into millimetres, each small interval is 1 mm. Find the whole centimetre immediately before the endpoint and count the remaining millimetre intervals.

Suppose a shelf bracket ends at the seventh millimetre mark after 12 cm. The whole part is 12 × 10 = 120 mm. Add 7 mm to obtain 127 mm, or 12.7 cm. Writing 12.07 cm would put the decimal in the wrong place. Record 127 mm so the unit and intended scale remain clear.

3. Add the imperial fraction to the whole inches

Johnson Level's reading guide explains the progressively shorter half-, quarter- and eighth-inch marks. Check the finest division on your tape: some show sixteenths, and some divide further. Do not assume every short line represents the same fraction on every tape.

On a tape divided into sixteenths, an endpoint six small intervals after 2 inches is 2 + 6/16 inches. Reduce 6/16 to 3/8, giving 2⅜ inches. This is a fraction of an inch, not 2.3 inches. Count intervals from the whole-inch mark rather than counting that starting line as one.

4. Why the end hook moves

Stanley explains that its hook's designed travel accounts for the thickness of the hook. Pulling it against an outside edge and pressing it against an inside face put the hook in different positions, so the thickness is accounted for in either measurement. Do not add an extra hook-thickness correction to a normal reading.

That explanation covers intentional movement; it does not prove that a bent hook or worn tape remains accurate. Inspect its condition and follow the maker's guidance. The scale-reading arithmetic here does not calibrate a tape or establish its accuracy class.

5. Record the dimension you will actually use

Keep the unit on the same line as the result, and repeat the measurement before transferring it to a cut or order. Avoid switching between the metric and imperial edges halfway through. For a room measured with a laser device, check its reference edge and displayed unit separately; the tape's hook procedure does not apply to that instrument.