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To convert a fractional inch to decimal inches, divide the numerator by the denominator: 3/8 in = 3 ÷ 8 = 0.375 in. Use the chart below for common fractions through 1 inch. Values are rounded to four decimal places; exact values are included in the longer reference table where rounding could change the last digit.
Fractional inches to decimal inches chart
This chart covers increments of 1/64 inch. Decimal values are rounded to four places using ordinary rounding; trailing zeros are kept for consistent display. For example, 5/32 inch is exactly 0.15625 inch and rounds to 0.1563 inch.
| Fraction | Decimal inches | Fraction | Decimal inches | Fraction | Decimal inches | Fraction | Decimal inches |
|---|---|---|---|---|---|---|---|
| 1/64 | 0.0156 | 17/64 | 0.2656 | 33/64 | 0.5156 | 49/64 | 0.7656 |
| 1/32 | 0.0313 | 9/16 | 0.5625 | 17/32 | 0.5313 | 25/32 | 0.7813 |
| 3/64 | 0.0469 | 19/64 | 0.2969 | 35/64 | 0.5469 | 51/64 | 0.7969 |
| 1/16 | 0.0625 | 5/8 | 0.6250 | 9/16 | 0.5625 | 13/16 | 0.8125 |
| 5/64 | 0.0781 | 21/64 | 0.3281 | 37/64 | 0.5781 | 53/64 | 0.8281 |
| 3/32 | 0.0938 | 11/16 | 0.6875 | 19/32 | 0.5938 | 27/32 | 0.8438 |
| 7/64 | 0.1094 | 23/64 | 0.3594 | 39/64 | 0.6094 | 55/64 | 0.8594 |
| 1/8 | 0.1250 | 3/4 | 0.7500 | 5/8 | 0.6250 | 7/8 | 0.8750 |
| 9/64 | 0.1406 | 25/64 | 0.3906 | 41/64 | 0.6406 | 57/64 | 0.8906 |
| 5/32 | 0.1563 | 13/16 | 0.8125 | 21/32 | 0.6563 | 29/32 | 0.9063 |
| 11/64 | 0.1719 | 27/64 | 0.4219 | 43/64 | 0.6719 | 59/64 | 0.9219 |
| 3/16 | 0.1875 | 7/8 | 0.8750 | 11/16 | 0.6875 | 15/16 | 0.9375 |
| 13/64 | 0.2031 | 29/64 | 0.4531 | 45/64 | 0.7031 | 61/64 | 0.9531 |
| 7/32 | 0.2188 | 15/32 | 0.4688 | 23/32 | 0.7188 | 31/32 | 0.9688 |
| 15/64 | 0.2344 | 31/64 | 0.4844 | 47/64 | 0.7344 | 63/64 | 0.9844 |
| 1/4 | 0.2500 | 1/2 | 0.5000 | 3/4 | 0.7500 | 1 | 1.0000 |
Note: The chart is arranged in grouped columns for compact reference, not in a single row-by-row counting sequence. Each fraction is a fraction of one inch.
How to convert a fraction to decimal inches
Divide the top number (numerator) by the bottom number (denominator):
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7/16 in = 7 ÷ 16 = 0.4375 in13/64 in = 13 ÷ 64 = 0.203125 in, or0.2031 inrounded to four decimal places.
The denominator tells you how many equal parts make up an inch. A 1/64-inch increment is exactly 0.015625 inch. For a mixed measurement, add the whole inches to the fraction: 2 3/8 in = 2 + (3 ÷ 8) = 2.375 in.
Common fractions and their decimal values
| Fraction | Exact decimal inches | Fraction | Exact decimal inches |
|---|---|---|---|
| 1/64 | 0.015625 | 1/2 | 0.500000 |
| 1/32 | 0.031250 | 9/16 | 0.562500 |
| 3/64 | 0.046875 | 5/8 | 0.625000 |
| 1/16 | 0.062500 | 11/16 | 0.687500 |
| 5/64 | 0.078125 | 3/4 | 0.750000 |
| 3/32 | 0.093750 | 13/16 | 0.812500 |
| 7/64 | 0.109375 | 7/8 | 0.875000 |
| 1/8 | 0.125000 | 15/16 | 0.937500 |
| 9/64 | 0.140625 | 1 | 1.000000 |
| 5/32 | 0.156250 | 3/16 | 0.187500 |
| 11/64 | 0.171875 | 13/64 | 0.203125 |
| 7/32 | 0.218750 | 1/4 | 0.250000 |
| 17/64 | 0.265625 | 9/32 | 0.281250 |
| 19/64 | 0.296875 | 5/16 | 0.312500 |
| 21/64 | 0.328125 | 11/32 | 0.343750 |
| 23/64 | 0.359375 | 3/8 | 0.375000 |
| 25/64 | 0.390625 | 13/32 | 0.406250 |
| 27/64 | 0.421875 | 7/16 | 0.437500 |
| 29/64 | 0.453125 | 15/32 | 0.468750 |
| 31/64 | 0.484375 | 17/32 | 0.531250 |
| 19/32 | 0.593750 | 21/32 | 0.656250 |
| 23/32 | 0.718750 | 31/32 | 0.968750 |
Decimal inches to fractions
To find the nearest ruler fraction, multiply the decimal by the denominator you want to use, round to the nearest whole number, then reduce the fraction if possible.
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For example, to convert 0.62 inch to the nearest 1/16 inch:
0.62 × 16 = 9.92- Round 9.92 to 10, giving 10/16 inch.
- Reduce 10/16 to 5/8 inch.
So 0.62 inch is approximately 5/8 inch to the nearest sixteenth. The answer can change with the chosen denominator: use the increment on your measuring tool or specified in the drawing, not an arbitrary one.
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Convert decimal inches to millimeters
Multiply decimal inches by 25.4. The international inch is exactly 25.4 millimeters, as specified by NIST.
| Inches | Millimeters |
|---|---|
| 0.125 in | 3.175 mm |
| 0.250 in | 6.35 mm |
| 0.375 in | 9.525 mm |
| 0.500 in | 12.7 mm |
| 1.000 in | 25.4 mm |
Keep the fraction or full decimal value through the calculation, then round the final millimeter result to the precision your specification requires. For example, convert 3/64 inch using its exact decimal, 0.046875: 0.046875 × 25.4 = 1.190625 mm. Rounding 0.047 inch first would give a slightly different result.
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Why decimal conversion charts can disagree
A fraction has a fixed mathematical value, but charts may display it differently because of precision or rounding. For example, 5/32 = 0.15625 exactly. To four decimal places, ordinary rounding gives 0.1563; truncating after four places gives 0.1562. Those are two display conventions, not two different inch measurements.
Other differences come from charts that show three, four, or six places, or that use a rounding convention suited to a particular technical standard. For measurements tied to tolerances, follow the drawing, specification, or applicable reporting standard. ASTM discusses rounding and significant digits as context-dependent; it does not establish one universal display rule for every use (ASTM rounding guidance). Calculate from the original fraction and round only the final displayed value.
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Choose precision for the job
| Situation | Practical approach |
|---|---|
| Quick reference | Three or four decimal places are often easy to read. |
| Tape measure or woodworking | Use the nearest 1/16, 1/32, or 1/64 inch that matches the tool and task. |
| Fabrication | Use the decimal places or fraction stated on the drawing or job specification. |
| Precision machining or inspection | Use the specified tolerance and reporting precision; do not infer accuracy from extra digits in a chart. |
| Exact calculation | Keep the fraction or full quotient until the final result. |
More decimal places do not make a measurement more accurate than the instrument or process that produced it. ASTM’s form-and-style guidance also distinguishes conversion from substituting a new rounded value in a specification. Do not silently replace a tolerance-controlled fractional dimension with an approximate decimal.
Do not confuse decimal inches with decimal feet
The unit is essential. 0.75 inch is three-quarters of an inch; 0.75 foot is 9 inches. Likewise, 0.375 inch equals 3/8 inch, while 0.375 foot equals 4.5 inches. A number entered into software that expects feet will not mean inches unless the unit is specified. Decimal inches are also not millimeters: 0.375 inch is 9.525 mm.
Write the unit with the value, such as 0.375 in, 0.375", or 3/8 in. Avoid a bare .375 or a feet mark when you mean inches. Surveying can involve a specialized historical survey-foot distinction; ordinary household, construction, woodworking, and shop conversions generally use the international inch. See NIST’s survey-foot guidance for that specialized context.
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A fractional drill designation can be converted with the same division—for example, a 1/4-inch drill has a nominal diameter of 0.2500 inch. But drill designations also include number and letter sizes: a number 1 drill is 0.2280 inch, while letter E is 0.2500 inch. These are tool-size labels, not fractional measurements, and a drill marked 1/4 inch does not guarantee a finished hole of exactly 0.2500 inch. Material, runout, and drilling method can affect the result. A separate LBL drill-size reference lists fractional, number, letter, and decimal equivalents.
Quick calculator method
For one-off conversions, enter the fraction as division in a calculator or spreadsheet—for example, =7/16 returns 0.4375. If converting to millimeters, multiply the unrounded result by 25.4. Confirm that any calculator, CAD field, or estimating program is set to inches rather than feet or millimeters before entering the result.
Quick Recap
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