How to convert between inches and metric

How to convert between inches and metric

TERMINOLOGY

Like all good stories this one starts with clarification of terminology and notation formats.

Inches can be written in a few ways:

  1. Fractions, as X-Y/Z". X is whole inches. Y/Z is then a fraction of an inch in addition to the whole inches.
  2. Decimals, as 0.00000...", with as many decimal places as you can accurately measure to.
  3. Thou, as .000", which is similar to decimals but specifically refers to thousandths of an inch and is often written without the leading zero.

Here's how 'half an inch' would be written in each:

  1. Fraction = 1/2"
  2. Decimal = 0.5"
  3. Thou = .500"

Millimetres (and other metric measurements) are more uniform, always being written as decimals. There is a minor difference in how the decimal is written between Europe and everywhere else:

  • Europe uses a , as a decimal place
  • Everywhere else uses a .

So three and a half millimetres would be written:

  • In Europe as 3,5mm
  • Everywhere else as 3.5mm

WHAT'S THE CALCULATION FROM INCHES TO METRIC?

Inches to mm

1 inch = 25.4mm

So, to convert inches to mm you first need the decimal version of how many inches you have, then you multiply it by 25.4.

For example, 1.5 inches = 1.5 x 25.4 = 38.1mm

If you need to convert a fraction of inches to mm, first find out what the fraction is in decimal form, and then use this in your calculation.

For example, what's 2-3/8? This represents 2 whole inches plus 3/8 of an inch. In the table of fractions we can see that 3/8 = 0.375, so added to the 2 we have 2.375 inches. Multiply this by 25.4 to get the answer, which is that 2-3/8" = 60.325mm.

Inches to cm

1 inch = 2.54cm

So, to convert inches to mm you first need the decimal version of how many inches you have, then you multiply it by 2.54.

For example, 15 inches = 15 x 2.54 = 38.1cm

Inches to m

1 inch = 0.0254m

So, to convert inches to mm you first need the decimal version of how many inches you have, then you multiply it by 0.0254.

For example, 150 inches = 150 x 0.0254 = 3.81m

WHAT'S THE CALCULATION FROM METRIC TO INCHES?

mm to inches

1mm = 0.0393701 inches

So, to convert mm to inches you need to multiply how many mm you have by 0.0393701.

For example, 15mm = 15 x 0.0393701 = 0.59" (to 2 decimal places)

cm to inches

1cm = 0.393701 inches

So, to convert mm to inches you need to multiply how many cm you have by 0.393701.

For example, 15cm = 15 x 0.393701 = 5.91" (to 2 decimal places)

m to inches

1m = 39.37 inches

So, to convert m to inches you need to multiply how many m you have by 39.37.

For example, 1.5m = 1.5 x 39.37 = 59.06" (to 2 decimal places)

INCH FRACTIONS TO MM

Here are the most common inch fractions converted to decimal inches and to mm. The smallest fraction we've given is 32nds - anything smaller than this tends to be represented as thou.

Inch /32 Inch /16 Inch /8 Inch /4 Inch /2 Whole Inches In words Inch Decimal mm (millimetres) cm (centimetres) m (metres)
1/32"           one thirty second 0.03125" 0.79mm 0.08cm 0.0008m
2/32" 1/16"         one sixteenth 0.0625" 1.59mm 0.16cm 0.0016m
3/32"           three thirty seconds 0.09375" 2.38mm 0.24cm 0.0024m
4/32" 2/16" 1/8"       one eighth 0.125" 3.18mm 0.32cm 0.0032m
5/32"           five thirty seconds 0.15625" 3.97mm 0.4cm 0.004m
6/32" 3/16"         three sixteenths 0.1875" 4.76mm 0.48cm 0.0048m
7/32"           seven thirty seconds 0.21875" 5.56mm 0.56cm 0.0056m
8/32" 4/16" 2/8" 1/4"     one quarter 0.25" 6.35mm 0.64cm 0.0064m
9/32"           nine thirty seconds 0.28125" 7.14mm 0.71cm 0.0071m
10/32" 5/16"         five sixteenths 0.3125" 7.94mm 0.79cm 0.0079m
11/32"           eleven thirty seconds 0.34375" 8.73mm 0.87cm 0.0087m
12/32" 6/16" 3/8"       three eighths 0.375" 9.53mm 0.95cm 0.0095m
13/32"           thirteen thirty seconds 0.40625" 10.32mm 1.03cm 0.0103m
14/32" 7/16"         seven sixteenths 0.4375" 11.11mm 1.11cm 0.0111m
15/32"           fifteen thirty seconds 0.46875" 11.91mm 1.19cm 0.0119m
16/32" 8/16" 4/8" 2/4" 1/2"   one half 0.5" 12.7mm 1.27cm 0.0127m
17/32"           seventeen thirty seconds 0.53125" 13.49mm 1.35cm 0.0135m
18/32" 9/16"         nine sixteenths 0.5625" 14.29mm 1.43cm 0.0143m
19/32"           nineteen thirty seconds 0.59375" 15.08mm 1.51cm 0.0151m
20/32" 10/16" 5/8"       five eighths 0.625" 15.88mm 1.59cm 0.0159m
21/32"           twenty one thirty seconds 0.65625" 16.67mm 1.67cm 0.0167m
22/32" 11/16"         eleven sixteenths 0.6875" 17.46mm 1.75cm 0.0175m
23/32"           twenty three thirty seconds 0.71875" 18.26mm 1.83cm 0.0183m
24/32" 12/16" 6/8" 3/4"     three quarters 0.75" 19.05mm 1.91cm 0.0191m
25/32"           twenty five thirty seconds 0.78125" 19.84mm 1.98cm 0.0198m
26/32" 13/16"         thirteen sixteenths 0.8125" 20.64mm 2.06cm 0.0206m
27/32"           twenty seven thirty seconds 0.84375" 21.43mm 2.14cm 0.0214m
28/32" 14/16" 7/8"       seven eighths 0.875" 22.23mm 2.22cm 0.0222m
29/32"           twenty nine thirty seconds 0.90625" 23.02mm 2.3cm 0.023m
30/32" 15/16"         fifteen sixteenths 0.9375" 23.81mm 2.38cm 0.0238m
31/32"           thirty one thirty seconds 0.96875" 24.61mm 2.46cm 0.0246m
32/32" 16/16" 8/8" 4/4" 2/2" 1" one 1" 25.4mm 2.54cm 0.0254m

THOU (THOUSANDTHS) OF AN INCH TO MM

"Thou" is used for smaller measurements under one inch when fractions don't offer the size required - tolerances, sheet thicknesses, machining parameters, threads. All sorts of small stuff. It can of course be expressed as a fraction, X/1000, but is written as a decimal. The leading 0 is usually omitted, so the measurement starts with a decimal. Here's how thou convert to metric:

Inch thou In words mm (millimetres) cm (centimetres)
.001 one thou 0.03mm 0.003cm
.002 two thou 0.05mm 0.005cm
.005 five thou 0.13mm 0.013cm
.010 ten thou 0.25mm 0.025cm
.015 fifteen thou 0.38mm 0.038cm
.020 twenty thou 0.51mm 0.051cm
.025 twenty five thou 0.64mm 0.064cm
.030 thirty thou 0.76mm 0.076cm
.035 thirty five thou 0.89mm 0.089cm
.040 forty thou 1.02mm 0.102cm
.045 forty five thou 1.14mm 0.114cm
.050 fifty thou 1.27mm 0.127cm
.055 fifty five thou 1.4mm 0.14cm
.060 sixty thou 1.52mm 0.152cm
.065 sixty five thou 1.65mm 0.165cm
.070 seventy thou 1.78mm 0.178cm
.075 seventy five thou 1.91mm 0.191cm
.080 eighty thou 2.03mm 0.203cm
.085 eighty five thou 2.16mm 0.216cm
.090 ninety thou 2.29mm 0.229cm
.095 ninety five thou 2.41mm 0.241cm
.100 one hundred thou 2.54mm 0.254cm
.110 one hundred and ten thou 2.79mm 0.279cm
.120 one hundred and twenty thou 3.05mm 0.305cm
.130 one hundred and thirty thou 3.3mm 0.33cm
.140 one hundred and forty thou 3.56mm 0.356cm
.150 one hundred and fifty thou 3.81mm 0.381cm
.160 one hundred and sixty thou 4.06mm 0.406cm
.170 one hundred and seventy thou 4.32mm 0.432cm
.180 one hundred and eighty thou 4.57mm 0.457cm
.190 one hundred and ninety thou 4.83mm 0.483cm
.200 two hundred thou 5.08mm 0.508cm
.250 two hundred and fifty thou 6.35mm 0.635cm
.300 three hundred thou 7.62mm 0.762cm
.400 four hundred thou 10.16mm 1.016cm
.500 five hundred thou 12.7mm 1.27cm
.600 six hundred thou 15.24mm 1.524cm
.700 seven hundred thou 17.78mm 1.778cm
.800 eight hundred thou 20.32mm 2.032cm
.900 nine hundred thou 22.86mm 2.286cm

WHOLE INCHES TO METRIC

Larger sheet sizes are often quoted in inches. Below is a chart showing the conversion between common inch and metre sizes.

Inches Feet mm (millimetres) cm (centimetres) m (metres)
1" 0.08' 25.4mm 2.54cm 0.0254m
2" 0.17' 50.8mm 5.08cm 0.0508m
3" 0.25' 76.2mm 7.62cm 0.0762m
4" 0.33' 101.6mm 10.16cm 0.1016m
5" 0.42' 127mm 12.7cm 0.127m
6" 0.5' 152.4mm 15.24cm 0.1524m
7" 0.58' 177.8mm 17.78cm 0.1778m
8" 0.67' 203.2mm 20.32cm 0.2032m
9" 0.75' 228.6mm 22.86cm 0.2286m
10" 0.83' 254mm 25.4cm 0.254m
11" 0.92' 279.4mm 27.94cm 0.2794m
12" 1' 304.8mm 30.48cm 0.3048m
18" 1.5' 457.2mm 45.72cm 0.4572m
19.69" 1.64' 500mm 50cm 0.5m
24" 2' 609.6mm 60.96cm 0.6096m
30" 2.5' 762mm 76.2cm 0.762m
36" 3' 914.4mm 91.44cm 0.9144m
39.37" 3.28' 1000mm 100cm 1m
40" 3.33' 1016mm 101.6cm 1.016m
47.24" 3.94' 1200mm 120cm 1.2m
48" 4' 1219.2mm 121.92cm 1.2192m
59.06" 4.92' 1500mm 150cm 1.5m
60" 5' 1524mm 152.4cm 1.524m
72" 6' 1828.8mm 182.88cm 1.8288m
78.74" 6.56' 2000mm 200cm 2m
84" 7' 2133.6mm 213.36cm 2.1336m
94.49" 7.87' 2400mm 240cm 2.4m
96" 8' 2438.4mm 243.84cm 2.4384m
108" 9' 2743.2mm 274.32cm 2.7432m
118.11" 9.84' 3000mm 300cm 3m
120" 10' 3048mm 304.8cm 3.048m

MM AND METRIC TO INCHES

Despite individual ones being tiny, millimetres are used for measuring everything from the very small all the way up to large sheets. Here's how mm convert to cm, m, inches and feet.

mm cm m Inch Fraction Thou Inch Decimal Feet
0.79mm 0.08cm 0.001m 1/32" .031 0.03  
1mm 0.1cm 0.001m   .039 0.04  
1.59mm 0.16cm 0.002m 1/16" .063 0.06  
2mm 0.2cm 0.002m   .079 0.08  
3.175mm 0.32cm 0.003m 1/8" .125 0.13  
4mm 0.4cm 0.004m   .157 0.16  
5mm 0.5cm 0.005m   .197 0.2  
6mm 0.6cm 0.006m   .236 0.24  
6.35mm 0.64cm 0.006m 1/4" .250 0.25  
7mm 0.7cm 0.007m   .276 0.28  
8mm 0.8cm 0.008m   .315 0.31  
9mm 0.9cm 0.009m   .354 0.35  
10mm 1cm 0.01m   .394 0.39  
12.7mm 1.27cm 0.013m 1/2" .500 0.5  
15mm 1.5cm 0.015m   .591 0.59  
20mm 2cm 0.02m   .787 0.79  
25.4mm 2.54cm 0.025m 1"   1 0.083
30mm 3cm 0.03m     1.18 0.098
38.1mm 3.81cm 0.038m 1-1/2"   1.5 0.125
40mm 4cm 0.04m     1.57 0.131
50mm 5cm 0.05m     1.97 0.164
50.8mm 5.08cm 0.051m 2"   2 0.167
100mm 10cm 0.1m     3.94 0.328
200mm 20cm 0.2m     7.87 0.656
300mm 30cm 0.3m     11.81 0.984
400mm 40cm 0.4m     15.75 1.312
500mm 50cm 0.5m     19.69 1.64
600mm 60cm 0.6m     23.62 1.969
1000mm 100cm 1m     39.37 3.281
1200mm 120cm 1.2m     47.24 3.937
2000mm 200cm 2m     78.74 6.562
2400mm 240cm 2.4m     94.49 7.874
3000mm 300cm 3m     118.11 9.843

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