What is 3 3/8 inches as a decimal?

3 + (3 ÷ 8) = 3.375 inches. The whole number stays, and the fraction becomes 0.375.

What is 3/8 inch as a decimal?

0.375 inches — divide 3 by 8. It's one of the most-looked-up conversions because it matches common drill and wrench sizes.

Why use decimal inches instead of fractions?

CNC controllers, CAD software, and spreadsheets all take decimals. Adding fractions like 5/16 + 7/32 by hand is awkward; 0.3125 + 0.21875 = 0.53125 is not.

What are the common fractional inch decimals?

1/8 = 0.125, 1/4 = 0.25, 3/8 = 0.375, 1/2 = 0.5, 5/8 = 0.625, 3/4 = 0.75, 7/8 = 0.875. Each sixteenth adds 0.0625.

How do I convert a fractional inch to millimetres?

Get the decimal first (whole + numerator ÷ denominator), then multiply by 25.4. 3 3/8 inches is 3.375 × 25.4 = 85.725 mm. The calculator shows the mm and cm results alongside the decimal.

Does the decimal ever repeat?

Only when the denominator has a factor other than 2. All the standard ruler fractions (halves through sixty-fourths) are powers of two, so they always terminate cleanly — 1/64 is exactly 0.015625.

Inches Fraction to Decimal Converter

Fractional inches are the language of tape measures, wrenches, and drill indexes. Decimal inches are the language of calculators, CNC controllers, and CAD software. This converter moves a measurement from the first world to the second — turning “3 and 3/8 inches” into 3.375 — and throws in the millimetre and centimetre equivalents so you don’t need a second tool to reach metric.

The fraction to decimal formula

For metric, multiply the decimal by 25.4 (mm) or 2.54 (cm).

Worked example

The calculator’s defaults are 3 whole inches plus 3/8.

In metric:

Inches Fraction to Decimal Converter worked example diagram — A visual read of the worked example above — the same numbers the calculator returns for its default inputs.

What Your Results Mean

The Decimal Inches result is the primary output you need for any calculation, CAD entry, or further conversion. The Millimeters and Centimeters results save you a separate conversion step when working with metric specifications or international suppliers.

Common fraction-to-decimal reference

Fraction	Decimal	mm
1/32	0.03125	0.794
1/16	0.0625	1.588
3/32	0.09375	2.381
1/8	0.125	3.175
5/32	0.15625	3.969
3/16	0.1875	4.763
7/32	0.21875	5.556
1/4	0.25	6.35
9/32	0.28125	7.144
5/16	0.3125	7.938
11/32	0.34375	8.731
3/8	0.375	9.525
13/32	0.40625	10.319
7/16	0.4375	11.113
15/32	0.46875	11.906
1/2	0.5	12.7
17/32	0.53125	13.494
9/16	0.5625	14.288
19/32	0.59375	15.081
5/8	0.625	15.875
21/32	0.65625	16.669
11/16	0.6875	17.463
23/32	0.71875	18.256
3/4	0.75	19.05
25/32	0.78125	19.844
13/16	0.8125	20.638
27/32	0.84375	21.431
7/8	0.875	22.225
29/32	0.90625	23.019
15/16	0.9375	23.813
31/32	0.96875	24.606
1	1.0	25.4

Why this matters in practice

When programming a CNC router, you enter dimensions in decimal inches (or mm). A cabinet side that’s “23 and 5/16 inches” becomes 23.3125 in your G-code. Getting this conversion wrong by even one sixteenth (0.0625”) means parts won’t fit, so precision matters.

Common mistakes

Adding the whole number to the fraction wrong. is , not rounded or .
Rounding the decimal too soon. Carry the full value (0.3125, not 0.31) when it feeds a cut list — a stack of small roundings adds up.
Mixing the mm factor with cm. Multiply decimal inches by 25.4 for millimetres and 2.54 for centimetres; swapping them is off by a factor of 10.
Reading a caliper’s decimal as a fraction directly. 0.313” is close to 5/16” (0.3125”), but not exactly — round to the nearest fraction only when a fraction is what you need.

To go the other direction and convert a decimal back to a tape-measure-friendly fraction, use the inches to fraction calculator. If you need the final value in metric only, the inches to mm converter and inches to cm converter work directly from decimal inch inputs.

A shortcut for sixteenths

Learn one number and every sixteenth follows: . Multiply it by the numerator. For :

The same idea works for eighths () and thirty-seconds (). is .

Fractional inches to decimal feet

Surveyors and some estimating software work in decimal feet. Convert to decimal inches first, then divide by 12. For 7 3/8 inches:

A wall that’s 10 ft 7 3/8 in long is therefore about 10.615 ft in decimal feet.

About the formula: Divide the numerator by the denominator and add to whole inches: decimal = whole + (numerator / denominator).