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Mechanical & dimensional reference

Fraction to Decimal Chart

Convert fractional inches, decimal inches, and millimeters, then find the nearest 1/8, 1/16, 1/32, or 1/64 inch fraction.

Range
0 to 1 in
Metric basis
1 in = 25.4 mm exact

Live converter

Convert Fractions, Decimals, and Millimeters

Enter a value once; exact conversions and the nearest standard inch fraction update automatically.

1/64-inch reference

Fraction to Decimal Conversion Chart

All increments from 0 through 1 inch, reduced to their simplest fraction with decimal-inch and millimeter equivalents.

Search by fraction, decimal, or millimeter value. Use the resolution filter to hide finer graduations.

Scroll horizontally to view additional columns and vertically to view additional rows. Column headers remain visible while scrolling.

Fractional inches from 0 through 1 inch in 1/64 increments with decimal-inch and millimeter equivalents.
Copy
00/640.0000000.000
1/641/640.0156250.397
1/322/640.0312500.794
3/643/640.0468751.191
1/164/640.0625001.588
5/645/640.0781251.984
3/326/640.0937502.381
7/647/640.1093752.778
1/88/640.1250003.175
9/649/640.1406253.572
5/3210/640.1562503.969
11/6411/640.1718754.366
3/1612/640.1875004.763
13/6413/640.2031255.159
7/3214/640.2187505.556
15/6415/640.2343755.953
1/416/640.2500006.350
17/6417/640.2656256.747
9/3218/640.2812507.144
19/6419/640.2968757.541
5/1620/640.3125007.938
21/6421/640.3281258.334
11/3222/640.3437508.731
23/6423/640.3593759.128
3/824/640.3750009.525
25/6425/640.3906259.922
13/3226/640.40625010.319
27/6427/640.42187510.716
7/1628/640.43750011.113
29/6429/640.45312511.509
15/3230/640.46875011.906
31/6431/640.48437512.303
1/232/640.50000012.700
33/6433/640.51562513.097
17/3234/640.53125013.494
35/6435/640.54687513.891
9/1636/640.56250014.288
37/6437/640.57812514.684
19/3238/640.59375015.081
39/6439/640.60937515.478
5/840/640.62500015.875
41/6441/640.64062516.272
21/3242/640.65625016.669
43/6443/640.67187517.066
11/1644/640.68750017.463
45/6445/640.70312517.859
23/3246/640.71875018.256
47/6447/640.73437518.653
3/448/640.75000019.050
49/6449/640.76562519.447
25/3250/640.78125019.844
51/6451/640.79687520.241
13/1652/640.81250020.638
53/6453/640.82812521.034
27/3254/640.84375021.431
55/6455/640.85937521.828
7/856/640.87500022.225
57/6457/640.89062522.622
29/3258/640.90625023.019
59/6459/640.92187523.416
15/1660/640.93750023.813
61/6461/640.95312524.209
31/3262/640.96875024.606
63/6463/640.98437525.003
164/641.00000025.400

Values are independently calculated. Millimeters use exactly 25.4 mm per inch. Display rounding does not change the exact underlying value.

Table actions

How to Use the Fraction to Decimal Chart

Use the converter when you have a value to translate or a decimal that needs the nearest practical fraction. Use the chart when you want to scan common 1/64-inch increments or compare exact equivalents.

  1. Choose the input format and enter a fraction, decimal inch value, or millimeter value.
  2. For decimal or metric inputs, choose the fraction resolution that matches the rule or shop reference you are using.
  3. Read the exact conversion first, then use the nearest-fraction value only when a rounded physical graduation is actually needed.
  4. Search the chart by fraction, decimal, or millimeter value; filter to coarser increments when you do not need all 64ths.

How to Convert a Fraction to a Decimal

Divide the numerator by the denominator. For example, 13/32 becomes 13 ÷ 32 = 0.40625 inch. Reducing a fraction changes its notation, not its value, so 24/64 and 3/8 both equal 0.375 inch.

For metric conversion, multiply the exact inch value by 25.4. Always convert from the exact fraction or canonical decimal, not from a rounded display value.

Conversion equations Decimal inches = numerator ÷ denominator Millimeters = inches × 25.4

The international inch is exactly 25.4 millimeters.

Fractional Inches to Millimeters

After converting the fraction to its exact inch value, multiply by exactly 25.4. For 3/8 inch: 0.375 × 25.4 = 9.525 mm. Keep the canonical value for calculations and round only for display.

Worked Conversion Examples

13/32 inch to decimal and mm

Assumption: the drawing dimension is exactly 13/32 in.

13 ÷ 32 = 0.40625 in.

0.40625 × 25.4 = 10.31875 mm.

Result: 13/32 in = 0.40625 in = 10.31875 mm. Display rounding should match the drawing tolerance, not imply extra accuracy.

0.33 inch to the nearest 1/64

Assumption: you need the closest mark on a 1/64-inch rule.

0.33 × 64 = 21.12, which rounds to 21.

21/64 = 0.328125 in.

Difference: −0.001875 in, so 21/64 is the nearest 1/64 mark but is not an exact representation of 0.33 in.

1/8, 1/16, 1/32, and 1/64 Inch Resolution

1/8 in
0.125 in spacing
1/16 in
0.0625 in spacing
1/32 in
0.03125 in spacing
1/64 in
0.015625 in spacing

Exact Values, Display Rounding, and Tolerances

Finer numerical resolution does not automatically mean the physical measurement is more accurate. A converted value should preserve the meaning of the original dimension and its tolerance. For example, changing a tape-measure reading to six decimal places does not make the original reading a six-decimal measurement.

The chart calculates millimeters from the exact rational inch value, not from the rounded decimal text shown on screen. For example, 3/16 in is exactly 4.7625 mm and displays as 4.763 mm in the three-decimal chart column.

Important: The nearest-fraction result is a rounding aid, not a tolerance recommendation or manufacturing acceptance criterion.

Using Fractional and Decimal Dimensions in Machining

Machining drawings and measuring tools often use decimal inches, while shop rules and some fastener or drill references use fractions. Convert the dimension first, then use an application-specific reference for the next task.

If you are selecting a drill rather than only converting a dimension, use the Drill Bit Size Chart. For threaded holes, continue to the Tap Drill Chart or UNC Thread Chart.

Conversion Method, Source, and Data Scope

Dataset scope: 0 through 1 inch in 1/64 increments, independently generated from exact fractional arithmetic.

The table is calculated rather than copied from a proprietary chart. Decimal inches come from the exact fraction, and millimeters use the exact international relationship of 25.4 mm per inch.

Dataset and Source-Check Details

Publisher
Turn2Engineering
Dataset
fraction-decimal-data-1.0.0
Canonical calculation
k/64, reduced by greatest common divisor
Metric conversion
Canonical inches × 25.4
Display precision
Decimal inches to 6 places; mm to 3 places using round-half-up for display only
Download rights
Formula-generated Turn2Engineering data may be downloaded as CSV
Known exclusion
No tolerance, fit, or manufacturing-process allowance is implied
Source check
Controlling NIST references verified during page research on September 4, 2026

Fraction to Decimal Chart FAQs

1/64 = 0.015625; when the fraction represents inches, it equals 0.396875 mm.

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