Inches to Fractions Converter
Instantly convert decimal inches to the nearest fraction, with metric equivalents, adjustable precision (½ to 1⁄64), a standard fraction reference chart, and a downloadable PDF report.
Uses the exact factor 1 in = 25.4 mm (international defined constant). Fractions are rounded to the nearest selected denominator (½ to 1⁄64) — for reference only.
| Fraction | Decimal (in) | Millimeters | Centimeters |
|---|
How to use the inches to fractions converter
Enter a decimal measurement, choose how fine a fraction you want, and read the answer as a tape measure would show it — reduced, with the rounding error stated, and the metric equivalent alongside.
Enter the decimal inches
Type the value from your calipers, plans, or CAD file — or tap a preset. Arrow keys step by 1/16.
Pick your precision
1/2 through 1/64. Match it to the tool you’re marking with — there’s no point converting to 1/64 for a tape marked in sixteenths.
Check the rounding error
The result shows how far the fraction sits from your true decimal, so you know whether it matters for this cut.
Read the chart & save a PDF
The 1/16 reference chart highlights your row, and the report includes every unit plus the full chart.
How the conversion is calculated
Turning a decimal into a fraction is four steps: split off the whole inches, multiply the remainder by the denominator you want, round to a whole numerator, then reduce. The metric side is a single exact constant — 1 inch = 25.4 mm, defined, not measured.
Worked example — 7.42 inches off a set of calipers
Split it: 7 whole inches + 0.42
At sixteenths: 0.42 × 16 = 6.72 → 7, giving 7 7/16" = 7.4375 — out by 0.0175 in
At thirty-seconds: 0.42 × 32 = 13.44 → 13, giving 7 13/32" = 7.40625 — out by 0.0138 in
At sixty-fourths: 0.42 × 64 = 26.88 → 27, giving 7 27/64" = 7.421875 — out by 0.0019 in
Three legitimate answers to the same measurement. The precision you pick is really a choice about how much error you can live with.
Inch fraction conversion charts
The lookups that come up most — the full sixteenths chart, awkward decimals at three precisions, millimeters read back as fractions, and what each precision level actually costs you in accuracy.
| Fraction | Decimal (in) | Millimeters | In 64ths |
|---|---|---|---|
| 1/16 | 0.0625 in | 1.588 mm | 4/64 |
| 1/8 | 0.1250 in | 3.175 mm | 8/64 |
| 3/16 | 0.1875 in | 4.763 mm | 12/64 |
| 1/4 | 0.2500 in | 6.350 mm | 16/64 |
| 5/16 | 0.3125 in | 7.938 mm | 20/64 |
| 3/8 | 0.3750 in | 9.525 mm | 24/64 |
| 7/16 | 0.4375 in | 11.113 mm | 28/64 |
| 1/2 | 0.5000 in | 12.700 mm | 32/64 |
| 9/16 | 0.5625 in | 14.288 mm | 36/64 |
| 5/8 | 0.6250 in | 15.875 mm | 40/64 |
| 11/16 | 0.6875 in | 17.463 mm | 44/64 |
| 3/4 | 0.7500 in | 19.050 mm | 48/64 |
| 13/16 | 0.8125 in | 20.638 mm | 52/64 |
| 7/8 | 0.8750 in | 22.225 mm | 56/64 |
| 15/16 | 0.9375 in | 23.813 mm | 60/64 |
| 1 inch | 1.0000 in | 25.400 mm | 64/64 |
Every one of these decimals is exact — no rounding anywhere in the column. That’s because each is a multiple of 0.0625, and it’s why the sixteenths are worth committing to memory.
| Decimal | Nearest 1/16 | Nearest 1/32 | Nearest 1/64 |
|---|---|---|---|
| 0.1 in | 1/8 | 3/32 | 3/32 |
| 0.2 in | 3/16 | 3/16 | 13/64 |
| 0.3 in | 5/16 | 5/16 | 19/64 |
| 0.333 in | 5/16 | 11/32 | 21/64 |
| 0.4 in | 3/8 | 13/32 | 13/32 |
| 0.6 in | 5/8 | 19/32 | 19/32 |
| 0.666 in | 11/16 | 21/32 | 43/64 |
| 0.7 in | 11/16 | 11/16 | 45/64 |
| 0.8 in | 13/16 | 13/16 | 51/64 |
| 0.9 in | 7/8 | 29/32 | 29/32 |
Notice how often the finer setting gives the same answer — 0.4 in is 13/32 at both 1/32 and 1/64. When that happens, the coarser fraction is the one to use: same accuracy, easier to mark.
| Millimeters | Decimal (in) | Nearest 1/16 | Nearest 1/32 |
|---|---|---|---|
| 1 mm | 0.0394 in | 1/16 | 1/32 |
| 2 mm | 0.0787 in | 1/16 | 3/32 |
| 3 mm | 0.1181 in | 1/8 | 1/8 |
| 4 mm | 0.1575 in | 3/16 | 5/32 |
| 5 mm | 0.1969 in | 3/16 | 3/16 |
| 6 mm | 0.2362 in | 1/4 | 1/4 |
| 8 mm | 0.3150 in | 5/16 | 5/16 |
| 10 mm | 0.3937 in | 3/8 | 13/32 |
| 12 mm | 0.4724 in | 1/2 | 15/32 |
| 15 mm | 0.5906 in | 9/16 | 19/32 |
| 20 mm | 0.7874 in | 13/16 | 25/32 |
| 25.4 mm | 1.0000 in | 1 inch | 1 inch |
Only the last row is exact. 25 mm is a touch under an inch — 63/64, close enough that the difference disappears into a pencil line, but it is not the same measurement.
| Precision | Step size | Step in mm | Worst-case error | Where it’s used |
|---|---|---|---|---|
| 1/2 | 0.5 in | 12.700 mm | ± 0.250 in | Rough estimates, ordering stock |
| 1/4 | 0.25 in | 6.350 mm | ± 0.125 in | Rough framing, demolition layout |
| 1/8 | 0.125 in | 3.175 mm | ± 0.0625 in | General carpentry, drywall |
| 1/16 | 0.0625 in | 1.588 mm | ± 0.03125 in | Standard tape measure — the default |
| 1/32 | 0.03125 in | 0.794 mm | ± 0.015625 in | Fine woodworking, joinery, machinist rules |
| 1/64 | 0.015625 in | 0.397 mm | ± 0.0078125 in | Precision layout, tooling, metalwork |
The worst case is always half a step. Rounding to 1/16 can move a measurement by up to 0.79 mm — smaller than most saw kerfs, larger than the tolerance on a well-fitted joint.
| Fraction | Decimal (in) | Millimeters | Turns up as |
|---|---|---|---|
| 1/16 in | 0.0625 | 1.588 mm | Smallest common tape mark |
| 1/8 in | 0.1250 | 3.175 mm | Hardboard, tile spacing, drill sizes |
| 3/16 in | 0.1875 | 4.763 mm | Bolt and drill sizes |
| 1/4 in | 0.2500 | 6.350 mm | Plywood, hex keys, chuck sizes |
| 5/16 in | 0.3125 | 7.938 mm | Socket and fastener sizes |
| 3/8 in | 0.3750 | 9.525 mm | Drywall, drill chucks, sheet goods |
| 1/2 in | 0.5000 | 12.700 mm | Drywall, plywood, pipe sizes |
| 5/8 in | 0.6250 | 15.875 mm | Fire-rated drywall, sheet goods |
| 3/4 in | 0.7500 | 19.050 mm | Plywood, hardwood stock, pipe |
Nominal sizes are not always actual sizes — sheet goods in particular are often milled a hair under the fraction on the label. Measure the material rather than trusting the name.
A tape measure divides each inch by halving four times — the half, the quarters, the eighths, the sixteenths — which is why the marks step down in length as they get finer. Converting a decimal means finding which of those marks it sits closest to, and reducing the result so it matches the label printed on the tape.
- Reducing changes the label, not the position — 6/16, 3/8 and 24/64 are the same mark on the same tape. The reduced form is the one people read.
- The error is never more than half a step — at sixteenths that ceiling is 1/32 of an inch, about 0.79 mm, whatever the decimal you started with.
- Metric never lands on a fraction — 25.4 mm to the inch means only exact multiples convert cleanly, so a millimeter measurement always rounds.
Everything the converter works out
One decimal gives you the fraction you can actually mark, the error you’re accepting, every related unit, and a chart you can keep at the bench.
The figures behind every inch
Built for anyone marking a decimal onto a tape
Plans, calipers and CAD all speak decimals. Tapes, squares and cut lists speak fractions. This is the translation that sits between the two, several times a day.
Taking a decimal dimension off a plan or a spreadsheet cut list and needing the mark you can actually make on the stock with the tape in your pocket.
- Round to what your tape shows
- Reduce before you write it down
- Allow for kerf on every cut
Reading decimal inches off digital calipers against a drawing dimensioned in fractions, or picking the fractional drill nearest a decimal hole size.
- 1 thou = 0.001 in = 0.0254 mm
- Use 1/64 for fractional drill matching
- Check the error against your tolerance
Working from instructions, hardware or components specified in millimeters while every tool in the shop is graduated in inches — or the reverse.
- Divide mm by 25.4, then round
- 1/16 in ≈ 1.6 mm as a mental check
- 25 mm is not an inch — it’s 63/64
7 tips for converting inches without errors
The slips that quietly put a cut out by a sixteenth — and the habits that catch them.
Inches to fractions FAQ
The conversion, tape-reading, and precision questions people ask most when a measurement arrives in the wrong form.
Split the number into whole inches and a decimal part, multiply the decimal part by the denominator you want, and round to the nearest whole number. That’s your numerator.
For 2.375 inches at sixteenths: 0.375 × 16 = 6, giving 6/16, which reduces to 3/8. The answer is 2 3/8 inches. Reducing by the greatest common divisor is what turns 6/16 into the 3/8 printed on a tape measure.
0.375 inches is exactly 3/8 of an inch, or 9.525 millimeters. No rounding is involved: 0.375 × 8 = 3 exactly.
Any decimal that’s a multiple of 0.015625 converts exactly at 1/64 or coarser — which covers every mark on a standard tape measure. That’s why fractions like 3/8, 5/16 and 11/16 all have clean decimal values.
1/16 inch is 0.0625 inches, or 1.5875 millimeters. It’s the smallest division marked on most standard US tape measures.
The rest of the ladder follows by halving: 1/2 is 0.5, 1/4 is 0.25, 1/8 is 0.125, 1/32 is 0.03125 and 1/64 is 0.015625 inches.
There are 16 sixteenths in one inch. A tape measure divides each inch by halving four times, which is why the marks get progressively shorter: the half, then the quarters, then the eighths, then the sixteenths.
The labels show the reduced fraction, so the mark at 8/16 reads as 1/2 and the mark at 12/16 reads as 3/4. Counting the small marks and reducing afterwards is the reliable way to read one.
2.5 inches is 2 1/2 inches, or 63.5 millimeters. The decimal part converts exactly at any denominator, so the precision setting makes no difference to the answer.
Written as an improper fraction it’s 5/2 inches, but mixed numbers are the standard on drawings and cut lists.
Divide the millimeters by 25.4 to get decimal inches, then round that decimal to the fraction you need. 100 ÷ 25.4 = 3.937 in, which rounds to 3 15/16 inches at sixteenths.
That one is unusually close — 3 15/16 inches is 99.99 mm, within a hundredth of a millimeter. Most metric values land less neatly, which is why the converter shows the rounding error alongside the fraction.
Because most decimals don’t land on a fraction mark. Rounding to the nearest 1/16 can shift the value by up to 1/32 of an inch — 0.03125 in, or about 0.79 mm.
The general rule is that the largest possible error is half a step, so rounding to 1/n can be out by up to 1/(2n). A finer denominator shrinks it: at 1/64 the worst case is 0.0078 in, under two tenths of a millimeter.
Most standard US tapes are marked to 1/16 inch. Some mark 1/32 across the first inch or two, and machinist rules are commonly graduated in 1/32 or 1/64.
There’s little value in converting to a precision your tool can’t show. Working from a tape marked in sixteenths, round to sixteenths and let the error figure tell you how much you gave up.
Reference Conversion Only — Rounded Results: This converter changes decimal inches into the nearest fraction at the denominator you select, using the exact constant 1 inch = 25.4 mm. Because most decimals do not fall on a fraction mark, the fractional result is rounded and may differ from your input by up to half of one step — up to 1/32 inch (about 0.79 mm) at a 1/16 setting. The converter reports this error with every result; check it against your own tolerance before cutting, drilling, or ordering material. Nominal fraction sizes for sheet goods, lumber, fasteners and pipe are naming conventions and often differ from actual dimensions, so measure the material itself rather than relying on its label. For reference purposes only.