Reading a Metric Tape Measure

  1. 1

    Identify the units

    Metric tapes show centimetres (cm) as the large numbered markings and millimetres (mm) as the small lines between. There are 10 millimetres in each centimetre.

  2. 2

    Read the measurement

    Find the last centimetre mark before your measurement point (the large number). Then count the small lines after it — each small line is 1mm. Example: if your measurement falls 3 small lines past the 14cm mark, the reading is 14.3cm or 143mm. Most tapes show millimetre values directly (so 143 means 143mm = 14.3cm).

Reading an Imperial Tape Measure

  1. 3

    Understand the fraction lines

    Imperial tapes divide each inch into fractions. The marking sizes tell you the fraction: the longest line between whole numbers = 1/2 inch. Next longest = 1/4 inch. Next = 1/8 inch. Shortest = 1/16 inch. Count how many of each division your measurement falls on after the last whole inch.

  2. 4

    Read the measurement

    Example: 3 inches plus 3 small lines past a 1/2 inch mark — if the tape is marked in 1/8ths, each small line is 1/8. So: 3 + 1/2 + 3/8 = 3 + 4/8 + 3/8 = 3 and 7/8 inches. Say this as "three and seven eighths inches" or write it as 3 7/8".

The Tape Hook — Why It Moves

The metal hook at the end of a tape measure moves slightly in and out — this is intentional, not a defect. The hook slides by exactly its own thickness so measurements are accurate whether you hook it over an edge (the hook adds its thickness from outside) or butt it against a surface (the hook recesses its thickness). Tapes that do not move are often inaccurate.

Common Markings to Know

  • Red numbers every 16 inches: Standard stud spacing in US/Australian framing (16" on centre)
  • Black diamonds every 19.2 inches: Truss spacing markers
  • Metric tapes often show 600mm markings: Standard Australian stud spacing
Measuring tipFor precise measurements, hook the tape end over one edge rather than holding it with your thumb — thumb width adds error. For internal measurements (measuring inside a box), butt the tape case against one side and add the case length (printed on the back of most tapes, usually 6cm or 3 inches) to the tape reading.

Frequently Asked Questions

Quality tape measures are accurate to within 1mm over their length when used correctly. Key sources of error: not holding the tape straight (sagging over long distances), pushing on the hook rather than hooking it, and reading from an angle. For critical measurements, take readings twice from different positions.
A ruler is rigid and typically 300mm (30cm) or 1 metre long — better for drawing straight lines and short precision measurements. A tape measure is flexible and retractable, useful for measuring curved surfaces, around objects and long distances. For most DIY and home tasks, a 5m or 8m tape measure is the primary measuring tool.