Reading a Metric Tape Measure

  1. 1

    Identify the large numbers (centimetres)

    The large numbers printed on the tape are centimetres (cm). The number 23 means 23 centimetres from the end of the tape.

  2. 2

    Count the small marks between centimetre numbers (millimetres)

    Between each pair of centimetre numbers, there are 9 small marks dividing the centimetre into 10 equal parts — each representing 1 millimetre (mm). There are 10mm in 1cm. Count how many of these small marks past the last whole centimetre your measurement falls on.

  3. 3

    Read the measurement

    If the end of the item lines up with the 3rd small mark after the 23cm mark, your measurement is 23cm and 3mm, written as 233mm or 23.3cm. Most Australian building and woodworking measurements use millimetres exclusively — saying “233 mil” rather than “23.3 centimetres.”

Reading an Imperial Tape Measure (Inches)

Some tape measures (especially older ones or those imported from the US) show inches. The largest marks are whole inches. Between inch marks, marks of decreasing size indicate fractions: the longest marks between inches = 1/2 inch. Medium marks = 1/4 inch. Shorter marks = 1/8 inch. Shortest marks = 1/16 inch.

The Hook at the End

The metal hook at the end of a tape measure is designed to move slightly — this is intentional, not a defect. When measuring from outside a surface (hooking onto an edge), the hook extends slightly. When measuring from inside (pressing against a surface), it retracts slightly. This movement compensates for the hook’s own thickness and ensures accurate measurement in both cases.

Tips for Accurate Measuring

  • Keep the tape straight — a bowed tape measures more than the actual distance
  • Read the tape at eye level directly above the measurement mark — reading at an angle causes parallax error
  • Measure twice, cut once — the oldest rule in carpentry
  • Mark with a sharp pencil, not a thick marker, for precise cutting
Metric vs imperial on Australian tapesMost Australian tape measures are metric with millimetres and centimetres. Many also have imperial (inches) on the reverse edge or bottom edge. For Australian construction and hardware stores, metric is standard — all timber, pipe, sheet material and hardware dimensions are in millimetres.

Frequently Asked Questions

Outside measurement (also called external measurement): hook the tape onto the end of the object and measure along its outside. The reading at the other end is the outside length. Inside measurement (also called internal measurement): press the tape’s body against one side of an internal space (like the inside of a drawer). The body of the tape case has its width printed on it (usually 50mm or 63mm). Read the tape at the other side and add the case width to get the total inside measurement. Many tape measures have the case width printed on them for this purpose.
For most household DIY (cutting timber, measuring rooms, hanging pictures): measuring to the nearest millimetre is sufficient. For fine woodworking and furniture: measure to the millimetre and aim to cut to within 0.5mm. For rough construction (framing, concrete formwork): the nearest 5mm is typically adequate. The key is consistency — use the same measuring technique and tool throughout a project to avoid cumulative errors.