TERMINOLOGY
Like all good stories this one starts with clarification of terminology and notation formats.
Inches can be written in a few ways:
- Fractions, as X-Y/Z". X is whole inches. Y/Z is then a fraction of an inch in addition to the whole inches.
- Decimals, as 0.00000...", with as many decimal places as you can accurately measure to.
- 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:
- Fraction = 1/2"
- Decimal = 0.5"
- 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 |