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MM to Inches Converter

Type a length in millimeters to get inches and the nearest ruler fraction, then see it at actual size on your screen.

Nearest 1/16 inch
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Centimeters

At actual size (top: cm, bottom: inches)

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MM to inches

How to convert mm to inches

One inch is exactly 25.4 millimeters, so to convert millimeters to inches, divide by 25.4. For example, 10 mm ÷ 25.4 = 0.3937 in. The converter also rounds to the nearest 1/16 inch, the smallest mark on most US rulers.

Related guides: Drill Bit Size Chart: Inch, Metric and Tap Drill Sizes · Screw and Bolt Size Chart: US and Metric

How to use it

  1. Type a length in millimeters; inches update as you type.
  2. Read the nearest 1/16 inch to find the mark on a US ruler, tape measure or drill-bit set.
  3. Tap Calibrate and match a card to see the length at real size.

Good to know

  • 1 mm = 0.03937 in, and 1 in = 25.4 mm exactly.
  • Close matches: 3 mm ≈ 1/8 in, 6 mm ≈ 1/4 in, 10 mm ≈ 3/8 in, 13 mm ≈ 1/2 in, 19 mm ≈ 3/4 in, 25 mm ≈ 1 in.
  • Quick mental math: 25 mm is just under 1 inch.

Conversion table

MillimetersInchesNearest 1/16 in1/64 in
10.03941/163/64
20.07871/165/64
30.11811/81/8
40.15753/165/32
50.19693/1613/64
60.23621/415/64
70.27561/49/32
80.3155/165/16
90.35433/823/64
100.39373/825/64
110.43317/167/16
120.47241/215/32
130.51181/233/64
140.55129/1635/64
150.59069/1619/32
160.62995/85/8
170.669311/1643/64
180.708711/1645/64
190.7483/43/4
200.787413/1625/32
210.826813/1653/64
220.86617/855/64
230.90557/829/32
240.944915/1615/16
250.9843163/64
261.023611 1/32
271.0631 1/161 1/16
281.10241 1/81 7/64
291.14171 1/81 9/64
301.18111 3/161 3/16
351.3781 3/81 3/8
401.57481 9/161 37/64
451.77171 3/41 49/64
501.96851 15/161 31/32
552.16542 3/162 11/64
602.36222 3/82 23/64
652.55912 9/162 9/16
702.75592 3/42 3/4
752.95282 15/162 61/64
803.14963 1/83 5/32
853.34653 3/83 11/32
903.54333 9/163 35/64
953.74023 3/43 47/64
1003.9373 15/163 15/16

Common mm sizes and where you see them

Millimeter sizes you run into every day, with the inch equivalent and the closest mark on a US ruler:

mmInchesRuler markWhere you see it
0.50.020≈ 1/64Mechanical pencil lead, the standard size
0.760.030≈ 1/32Thickness of a credit card
1.750.069≈ 1/163D printer filament, the most common diameter
3.50.138≈ 9/64Headphone plug (the "3.5 mm jack")
60.236≈ 1/4M6 bolt diameter (takes a 10 mm wrench)
80.315≈ 5/16M8 bolt diameter (takes a 13 mm wrench)
100.394≈ 3/8One of the most used socket sizes on cars and bikes
12.70.5001/2Exactly 1/2 inch
190.748≈ 3/4Wrench that also fits 3/4 in nuts
25.41.0001Exactly 1 inch
351.378≈ 1 3/8Width of 35 mm camera film

See the length at actual size

The rulers on this page are drawn at real size once your screen is calibrated. Tap Calibrate and match any bank card (accurate to about ±0.5%), or choose your phone or laptop model. It takes about 20 seconds and is saved for next time.

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FAQ

Frequently asked questions

1 mm is 0.03937 inches, about 1/25 of an inch. It takes 25.4 mm to make one inch.

Inches = millimeters ÷ 25.4. For example, 50 mm ÷ 25.4 = 1.9685 inches.

10 mm is 0.3937 inches, which is closest to 3/8 inch (0.375 in) on a ruler marked in sixteenths. The difference is under 0.5 mm.

Open the mm ruler, calibrate it with a bank card and hold the object against the edge of the screen. Each small line is 1 mm.

Exactly 25.4 mm. The inch has been defined as 25.4 millimeters since 1959, so 1/2 inch is 12.7 mm and 1/4 inch is 6.35 mm.

No, much smaller. An inch is 25.4 times longer than a millimeter. One millimeter is a little thicker than a credit card (0.76 mm) and a little thinner than a US dime (1.35 mm).

Divide by 25.4, multiply by 16 and round to a whole number: that's the number of sixteenths. For 5 mm: 5 ÷ 25.4 × 16 = 3.15, so about 3/16 inch. The converter above does this for you.

3 mm ≈ 1/8 in (0.118), 6 mm ≈ 1/4 in (0.236), 10 mm ≈ 3/8 in (0.394), 13 mm ≈ 1/2 in (0.512), 19 mm ≈ 3/4 in (0.748) and 25 mm ≈ 1 in (0.984).

On a metric ruler each small line is 1 mm, the slightly longer line halfway between numbers is 5 mm, and each numbered line is a centimeter (10 mm). Count the centimeters, multiply by 10 and add the small lines: 3 cm plus 4 lines is 34 mm.