How to Read a Tape Measure
To read a tape measure, find the last whole inch before the end of what you are measuring, then count the small marks after it: each inch is divided into 16 parts, and the length of each mark tells you its fraction. The longest mark between the inches is 1/2 in, the next are the quarters, then the eighths, and the shortest are the sixteenths. Read the whole inches, add the fraction, and reduce it: 3 inches plus 10 sixteenths is 3 10/16 = 3 5/8 in. The printable cheat sheet below shows every inch mark in 16ths.
The marks on a tape measure
| Mark | Length of the line | Fractions it shows |
|---|---|---|
| Inch | Longest, with a number | 1, 2, 3 ... in |
| Half inch | Second longest | 1/2 |
| Quarter inch | Third longest | 1/4, 3/4 |
| Eighth inch | Fourth longest | 1/8, 3/8, 5/8, 7/8 |
| Sixteenth inch | Shortest | 1/16, 3/16, 5/16 ... 15/16 |
Some tapes, mostly for fine work, also show 1/32 in in the first few inches.
Reading a measurement step by step
- Hook the end over the edge of the board, or push it flat against the surface.
- Find the last whole inch before the edge of what you are measuring: say 7.
- Count the sixteenths from that inch to the edge: say 5.
- Write it as a fraction and reduce it if you can: 5/16 cannot be reduced, so the size is 7 5/16 in. Had you counted 12, it would be 12/16 = 3/4, so 7 3/4 in.
A quick way to reduce: if the number of sixteenths is even, halve both numbers (12/16 → 6/8 → 3/4) until the top is odd.
Fractions to decimals and mm
| Sixteenths | Fraction | Decimal | mm |
|---|---|---|---|
| 2 | 1/8 | 0.125 | 3.2 |
| 4 | 1/4 | 0.25 | 6.4 |
| 6 | 3/8 | 0.375 | 9.5 |
| 8 | 1/2 | 0.5 | 12.7 |
| 10 | 5/8 | 0.625 | 15.9 |
| 12 | 3/4 | 0.75 | 19.1 |
| 14 | 7/8 | 0.875 | 22.2 |
The full chart down to 1/64 in, with a converter, is on our inches to mm chart.
Feet, stud marks and diamonds
- Feet: after 12 in, most tapes show 1F, 2F or switch to feet and inches (1' 1", 1' 2" ...). 30 in reads as 2' 6".
- Red numbers every 16 in: the standard spacing of studs and joists (16, 32, 48 ...).
- Black diamonds every 19 3/16 in: truss and joist spacing that fits five in 8 ft.
The hook and inside measurements
The metal hook moves by its own thickness, about 1/16 in. Pulled over an edge it slides out; pushed against a wall it slides in, so both readings start from true zero. Do not bend it back or the tape stops being accurate. For an inside measurement, like a cabinet opening, push the case into the corner and add the length of the case printed on it (often 3 in), or measure from the 10 in mark and subtract 10.
Reading a metric tape measure
Metric tapes are simpler: each numbered line is a centimetre (10 mm), each small line a millimetre, and a slightly longer line marks 5 mm. Read the centimetres, then count the millimetres: 45 cm and 3 marks is 453 mm. Woodworkers and cabinetmakers usually work in millimetres only, which removes the fractions altogether.
Measuring for a cut list
Measure twice, write the size down straight away, and say which dimension is the length and which the width, especially for parts with grain. Cut to the waste side of the line: the saw blade removes about 1/8 in (3 mm), the kerf. When you are ready, type your parts into the free cut list optimizer in inches with fractions or in millimetres.
Frequently asked questions
How do you read the small lines on a tape measure?
Each inch is split into 16 parts. The longest line in the middle is 1/2 in, the next longest are 1/4 and 3/4, then the eighths, and the shortest lines are the sixteenths. Count the sixteenths from the last whole inch and reduce the fraction.
What do the red numbers on a tape measure mean?
They mark every 16 in, the usual spacing of wall studs and floor joists, so you can lay out framing quickly. Some tapes also mark every foot in red.
What are the black diamonds on a tape measure?
Truss marks every 19 3/16 in (19.2 in): five of them fit in 8 ft, the spacing used for some engineered joists and trusses.
Why does the hook at the end of a tape measure move?
On purpose. It slides by its own thickness so the reading is right both when you hook it over an edge and when you push it against a wall.
How do you read a metric tape measure?
Each numbered line is a centimetre and each small line a millimetre, with a longer line at 5 mm. Read the last centimetre and add the millimetres: 23 cm and 7 small lines is 237 mm.
How do you read a tape measure in millimeters?
On a metric tape every small line is 1 millimeter, every longer line 5 mm, and the numbered lines are centimetres (10 mm). Read the last centimetre number, then count the millimeter lines after it: 23 cm and 4 lines is 234 mm.