Millimeters to Inches

Convert millimeters to inches instantly, with a reference table.

Millimeters to Inches conversion table
Millimeters (mm)Inches (in)
10.04
20.08
30.12
40.16
50.2
60.24
70.28
80.31
90.35
100.39
Formula: 1 mm = 0.03937 in. To convert, multiply your millimeters figure by 0.03937.

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About the Millimeters to Inches

Millimeters to Inches is a free converter that turns a metric length in millimeters into its equivalent in inches. The conversion rests on one fixed international definition: one inch is exactly 25.4 millimeters. So to go from mm to inches you simply divide by 25.4, which is the same as multiplying by 0.0393701. Enter a value such as 100 mm and the tool returns 3.937 in. Because the 25.4 factor is an exact, internationally agreed constant rather than an approximation, the only thing that limits precision is how many decimal places you choose to display.

Reach for this tool whenever a measurement arrives in metric but your task, parts, or tools are imperial. Hardware is a classic case: an M4 screw is 4 mm in diameter, and you may need its closest inch equivalent to match a drill bit or fastener chart. The same situation shows up with firearm calibers (a 7.62 mm bore equals .30 inch), jewelry wire gauges, phone and TV screen dimensions, woodworking stock, 3D-print tolerances, and product specs sourced from overseas suppliers. Anyone bridging a metric drawing and an imperial workshop converts mm to inches constantly.

Under the hood the math is a single division, but real work often needs a fractional inch rather than a decimal. To express the result as a fraction, multiply the decimal part by the denominator you want, then round. For sixteenths, multiply by 16 and round to the nearest whole number; for finer machining or cabinetry, use 32. For example, 12 mm is 0.4724 in, and 0.4724 multiplied by 16 is about 7.6, which rounds to 8, giving roughly 1/2 inch on a tape measure. Use 1/16 for framing and household tapes, 1/32 for furniture and drill-bit selection.

Everything runs locally in your browser, so the numbers you type are never uploaded or stored on a server. That keeps the converter instant and private, which matters when you are checking confidential part dimensions or pricing specs. The decimal answer is mathematically exact for the precision shown; rounding only occurs when you ask for a fraction. If two decimals are not enough for a tight tolerance, request more places before rounding to a fraction, because rounding early can shift you a full sixteenth off the true value.

Frequently asked questions

How many millimeters are in one inch?

Exactly 25.4 millimeters. This is an internationally defined exact value, not a rounded estimate, so it holds for every conversion.

What is the formula to convert mm to inches?

Divide the millimeter value by 25.4, or equivalently multiply it by 0.0393701. For example, 50 mm divided by 25.4 equals about 1.9685 inches.

How do I turn the result into a fraction of an inch?

Take the decimal inches, multiply the value by 16 (or 32 for finer work), and round to the nearest whole number to get the numerator over that denominator. For instance, 0.47 in times 16 is about 8, giving roughly 8/16, or 1/2 inch.

Is converting mm to inches exact or approximate?

The division by 25.4 is exact; the only rounding is in how many decimal places or how fine a fraction you display. Most mm values produce a long repeating decimal, so a clean inch number is rare.

What is 10 mm in inches?

10 mm equals about 0.3937 inches, which is just under 13/32 inch on a tape measure. As a quick mental shortcut, every 25.4 mm is one inch.

From our blog

Cooking Conversions Made Simple: Cups, Grams, and Why Your Scale Wins

By the Super Simple Digital Tools Team · Updated June 2026

Almost every cook hits the same wall eventually: a recipe you want to make is written in units your kitchen does not speak. Maybe it is an American cake recipe listing cups and sticks of butter, or a European one in grams and millilitres. The good news is that conversion is mostly arithmetic, and once you understand which numbers are fixed and which depend on the ingredient, you can adapt any recipe with confidence.

Start with the volume measures, because these never change. A teaspoon is a third of a tablespoon, a tablespoon is a sixteenth of a US cup, and a US cup is just under 237 millilitres. These ratios hold no matter what is being measured, whether it is water, oil or vanilla extract. So if a recipe wants a quarter cup of milk and you only have measuring spoons, you can confidently use four tablespoons. This is the easy, predictable half of cooking conversion.

The trickier half is moving between volume and weight. Grams and ounces measure mass, and mass depends on how densely an ingredient packs into a cup. This is why a single cup measurement can equal wildly different weights: roughly 120 grams for fluffy all-purpose flour but around 200 grams for granulated sugar, which packs tightly. A converter that ignores the ingredient and uses one fixed gram-per-cup figure will be wrong for almost everything, which is why selecting the actual ingredient matters so much.

Be aware that the cup itself is not universal. The US cup is about 240 millilitres, the metric cup used across Australia and New Zealand is 250 millilitres, and the historic UK imperial cup was larger still at about 284 millilitres. For a soup or a stew this rarely matters. For a delicate sponge or a bread dough, where the balance of flour to liquid is critical, using the wrong cup standard can leave you with a batter that is too wet or a cake that refuses to rise.

If you take one thing away, let it be this: weighing beats measuring by volume. Professional bakers work in grams precisely because a scale removes the guesswork of how firmly you packed the cup or whether the flour had settled. A converter is perfect for translating a recipe quickly and for everyday cooking, but when accuracy counts, convert the volume amounts to grams once, then weigh them. Your results will be far more consistent from one batch to the next.

  • Always choose the specific ingredient before converting cups to grams; flour, sugar and butter all weigh different amounts per cup.
  • Remember the core spoon ratios: 3 teaspoons make a tablespoon and 16 tablespoons make a US cup, so you can swap between them without a tool.
  • Check whether a recipe uses US (about 240 ml) or metric (250 ml) cups before baking, since the difference can affect rise and texture.
  • For the most reliable baking, convert your volume measurements to grams once and weigh the ingredients on a digital scale instead of scooping.

Read the full guide →

Tool by the Super Simple Digital Tools Team. Reviewed by our editorial team. Free to use, no signup required.

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