How do you convert a decimal to inches and fractions?
0.375" is 3/8". Multiply by 16, round, and put it over 16 — then simplify. Every sixteenth as a decimal and in millimetres.
Multiply by 16 and round: 0.375 × 16 = 6, so 0.375" is 3/8".
A tape is marked in sixteenths, so sixteenths is the answer you actually want. For finer work multiply by 32 or 64 instead — the method does not change, only the denominator.
How that is worked out
- Multiply the decimal by the denominator you want — 16 for a tape measure, 32 or 64 for machine work.
- Round to a whole number and put it over that denominator: 6/16.
- Simplify by halving top and bottom while both stay whole: 6/16 → 3/8". That is the form a tape is actually marked in.
Every sixteenth, as a decimal and in millimetres
| Fraction | Decimal | Millimetres | In 32nds | In 64ths |
|---|---|---|---|---|
| 1/16" | 0.0625 | 1.59 | 2/32 | 4/64 |
| 1/8" | 0.1250 | 3.17 | 4/32 | 8/64 |
| 3/16" | 0.1875 | 4.76 | 6/32 | 12/64 |
| 1/4" | 0.2500 | 6.35 | 8/32 | 16/64 |
| 5/16" | 0.3125 | 7.94 | 10/32 | 20/64 |
| 3/8" | 0.3750 | 9.52 | 12/32 | 24/64 |
| 7/16" | 0.4375 | 11.11 | 14/32 | 28/64 |
| 1/2" | 0.5000 | 12.70 | 16/32 | 32/64 |
| 9/16" | 0.5625 | 14.29 | 18/32 | 36/64 |
| 5/8" | 0.6250 | 15.88 | 20/32 | 40/64 |
| 11/16" | 0.6875 | 17.46 | 22/32 | 44/64 |
| 3/4" | 0.7500 | 19.05 | 24/32 | 48/64 |
| 13/16" | 0.8125 | 20.64 | 26/32 | 52/64 |
| 7/8" | 0.8750 | 22.22 | 28/32 | 56/64 |
| 15/16" | 0.9375 | 23.81 | 30/32 | 60/64 |
| 1" | 1.0000 | 25.40 | 32/32 | 64/64 |
Worth knowing
- Round to what you can actually cut. A sixteenth is the honest limit of a tape and a pencil line; a thirty-second is realistic at a table saw with a good rule; sixty-fourths belong to machine setups and feeler gauges.
- The inch is defined as exactly 25.4 mm, so the millimetre column is exact rather than approximate. It is one of the few conversions in this trade that is not a rounding.
- Watch for decimals that do not land on a sixteenth. 0.333" is a third of an inch and is not any fraction on a tape — it is between 5/16" and 3/8", and which one you take depends on whether the part has to fit inside something.
- A part that has to fit inside something rounds down; a clearance or a jig setting rounds up. Rounding to nearest is right for a dimension and wrong for both of those.
Work out your own numbers
- Inch fraction calculator
Add or subtract two measurements written the way a tape shows them, read to the nearest sixteenth, thirty-second or sixty-fourth.
- Board cut calculator
How many pieces of one length come out of a board of another, with the kerf charged between cuts and the leftover shown.
Related questions
- What is 0.375 inches as a fraction?
- 3/8". Multiply 0.375 by 16 to get 6, which is 6/16, and halving top and bottom twice gives 3/8. The same method works for any decimal — the only decision is which denominator you want to land on.
- How do I convert a decimal that isn't an exact fraction?
- Round it, and round it in the direction the part needs. 0.40" × 16 = 6.4, so the nearest sixteenth is 6/16 — that is 3/8", about 0.025" under. If the part has to fit inside something, take the smaller fraction; if it is a clearance or a jig setting, take the larger.
- How many millimetres is an inch?
- Exactly 25.4, by definition since 1959. That makes it one of the few conversions in the trade that is exact rather than a rounding — 1/16" is precisely 1.5875 mm, not approximately.