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Engineering Conversion Chart
Inch fractions to decimals and mm, mm to inch, multiply-by factors for pressure, torque, power, force, stress and more, hardness conversions HRC / HRB / HV / HB with typical material hardness, and temperature.
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1 inch = 25.4 mm exactly. Hardness conversions are approximate and for steel only.
Fractions 1/64 - 1/2 inch
| Inch | Decimal in | mm |
|---|
| 1/64" | 0.0156 | 0.397 |
| 1/32" | 0.0312 | 0.794 |
| 3/64" | 0.0469 | 1.191 |
| 1/16" | 0.0625 | 1.587 |
| 5/64" | 0.0781 | 1.984 |
| 3/32" | 0.0938 | 2.381 |
| 7/64" | 0.1094 | 2.778 |
| 1/8" | 0.1250 | 3.175 |
| 9/64" | 0.1406 | 3.572 |
| 5/32" | 0.1562 | 3.969 |
| 11/64" | 0.1719 | 4.366 |
| 3/16" | 0.1875 | 4.762 |
| 13/64" | 0.2031 | 5.159 |
| 7/32" | 0.2188 | 5.556 |
| 15/64" | 0.2344 | 5.953 |
| 1/4" | 0.2500 | 6.350 |
| 17/64" | 0.2656 | 6.747 |
| 9/32" | 0.2812 | 7.144 |
| 19/64" | 0.2969 | 7.541 |
| 5/16" | 0.3125 | 7.938 |
| 21/64" | 0.3281 | 8.334 |
| 11/32" | 0.3438 | 8.731 |
| 23/64" | 0.3594 | 9.128 |
| 3/8" | 0.3750 | 9.525 |
| 25/64" | 0.3906 | 9.922 |
| 13/32" | 0.4062 | 10.319 |
| 27/64" | 0.4219 | 10.716 |
| 7/16" | 0.4375 | 11.112 |
| 29/64" | 0.4531 | 11.509 |
| 15/32" | 0.4688 | 11.906 |
| 31/64" | 0.4844 | 12.303 |
| 1/2" | 0.5000 | 12.700 |
Fractions 33/64 - 1 inch
| Inch | Decimal in | mm |
|---|
| 33/64" | 0.5156 | 13.097 |
| 17/32" | 0.5312 | 13.494 |
| 35/64" | 0.5469 | 13.891 |
| 9/16" | 0.5625 | 14.287 |
| 37/64" | 0.5781 | 14.684 |
| 19/32" | 0.5938 | 15.081 |
| 39/64" | 0.6094 | 15.478 |
| 5/8" | 0.6250 | 15.875 |
| 41/64" | 0.6406 | 16.272 |
| 21/32" | 0.6562 | 16.669 |
| 43/64" | 0.6719 | 17.066 |
| 11/16" | 0.6875 | 17.462 |
| 45/64" | 0.7031 | 17.859 |
| 23/32" | 0.7188 | 18.256 |
| 47/64" | 0.7344 | 18.653 |
| 3/4" | 0.7500 | 19.050 |
| 49/64" | 0.7656 | 19.447 |
| 25/32" | 0.7812 | 19.844 |
| 51/64" | 0.7969 | 20.241 |
| 13/16" | 0.8125 | 20.637 |
| 53/64" | 0.8281 | 21.034 |
| 27/32" | 0.8438 | 21.431 |
| 55/64" | 0.8594 | 21.828 |
| 7/8" | 0.8750 | 22.225 |
| 57/64" | 0.8906 | 22.622 |
| 29/32" | 0.9062 | 23.019 |
| 59/64" | 0.9219 | 23.416 |
| 15/16" | 0.9375 | 23.812 |
| 61/64" | 0.9531 | 24.209 |
| 31/32" | 0.9688 | 24.606 |
| 63/64" | 0.9844 | 25.003 |
| 1" | 1.0000 | 25.400 |
1 - 3 inch
| Inch | Decimal in | mm |
|---|
| 1-1/16" | 1.0625 | 26.987 |
| 1-1/8" | 1.1250 | 28.575 |
| 1-3/16" | 1.1875 | 30.162 |
| 1-1/4" | 1.2500 | 31.750 |
| 1-5/16" | 1.3125 | 33.337 |
| 1-3/8" | 1.3750 | 34.925 |
| 1-7/16" | 1.4375 | 36.512 |
| 1-1/2" | 1.5000 | 38.100 |
| 1-9/16" | 1.5625 | 39.688 |
| 1-5/8" | 1.6250 | 41.275 |
| 1-11/16" | 1.6875 | 42.862 |
| 1-3/4" | 1.7500 | 44.450 |
| 1-13/16" | 1.8125 | 46.037 |
| 1-7/8" | 1.8750 | 47.625 |
| 1-15/16" | 1.9375 | 49.212 |
| 2" | 2.0000 | 50.800 |
| 2-1/16" | 2.0625 | 52.387 |
| 2-1/8" | 2.1250 | 53.975 |
| 2-3/16" | 2.1875 | 55.562 |
| 2-1/4" | 2.2500 | 57.150 |
| 2-5/16" | 2.3125 | 58.737 |
| 2-3/8" | 2.3750 | 60.325 |
| 2-7/16" | 2.4375 | 61.912 |
| 2-1/2" | 2.5000 | 63.500 |
| 2-9/16" | 2.5625 | 65.087 |
| 2-5/8" | 2.6250 | 66.675 |
| 2-11/16" | 2.6875 | 68.263 |
| 2-3/4" | 2.7500 | 69.850 |
| 2-13/16" | 2.8125 | 71.438 |
| 2-7/8" | 2.8750 | 73.025 |
| 2-15/16" | 2.9375 | 74.612 |
| 3" | 3.0000 | 76.200 |
Millimetres to inches
| mm | inch | mm | inch | mm | inch | mm | inch |
|---|
| 1 | 0.0394 | 26 | 1.0236 | 51 | 2.0079 | 76 | 2.9921 |
| 2 | 0.0787 | 27 | 1.0630 | 52 | 2.0472 | 77 | 3.0315 |
| 3 | 0.1181 | 28 | 1.1024 | 53 | 2.0866 | 78 | 3.0709 |
| 4 | 0.1575 | 29 | 1.1417 | 54 | 2.1260 | 79 | 3.1102 |
| 5 | 0.1969 | 30 | 1.1811 | 55 | 2.1654 | 80 | 3.1496 |
| 6 | 0.2362 | 31 | 1.2205 | 56 | 2.2047 | 81 | 3.1890 |
| 7 | 0.2756 | 32 | 1.2598 | 57 | 2.2441 | 82 | 3.2283 |
| 8 | 0.3150 | 33 | 1.2992 | 58 | 2.2835 | 83 | 3.2677 |
| 9 | 0.3543 | 34 | 1.3386 | 59 | 2.3228 | 84 | 3.3071 |
| 10 | 0.3937 | 35 | 1.3780 | 60 | 2.3622 | 85 | 3.3465 |
| 11 | 0.4331 | 36 | 1.4173 | 61 | 2.4016 | 86 | 3.3858 |
| 12 | 0.4724 | 37 | 1.4567 | 62 | 2.4409 | 87 | 3.4252 |
| 13 | 0.5118 | 38 | 1.4961 | 63 | 2.4803 | 88 | 3.4646 |
| 14 | 0.5512 | 39 | 1.5354 | 64 | 2.5197 | 89 | 3.5039 |
| 15 | 0.5906 | 40 | 1.5748 | 65 | 2.5591 | 90 | 3.5433 |
| 16 | 0.6299 | 41 | 1.6142 | 66 | 2.5984 | 91 | 3.5827 |
| 17 | 0.6693 | 42 | 1.6535 | 67 | 2.6378 | 92 | 3.6220 |
| 18 | 0.7087 | 43 | 1.6929 | 68 | 2.6772 | 93 | 3.6614 |
| 19 | 0.7480 | 44 | 1.7323 | 69 | 2.7165 | 94 | 3.7008 |
| 20 | 0.7874 | 45 | 1.7717 | 70 | 2.7559 | 95 | 3.7402 |
| 21 | 0.8268 | 46 | 1.8110 | 71 | 2.7953 | 96 | 3.7795 |
| 22 | 0.8661 | 47 | 1.8504 | 72 | 2.8346 | 97 | 3.8189 |
| 23 | 0.9055 | 48 | 1.8898 | 73 | 2.8740 | 98 | 3.8583 |
| 24 | 0.9449 | 49 | 1.9291 | 74 | 2.9134 | 99 | 3.8976 |
| 25 | 0.9843 | 50 | 1.9685 | 75 | 2.9528 | 100 | 3.9370 |
Engineering units
| Quantity | From | To | Multiply by | Back: multiply by |
|---|
| Length | inch | mm | 25.4 | 0.03937 |
| thou (0.001 in) | micron (µm) | 25.4 | 0.03937 |
| foot | metre | 0.3048 | 3.2808 |
| mile | km | 1.6093 | 0.6214 |
| Area | sq inch | mm2 | 645.16 | 0.00155 |
| sq foot | m2 | 0.0929 | 10.764 |
| Volume | cu inch | cm3 (cc) | 16.387 | 0.06102 |
| UK gallon | litre | 4.5461 | 0.2200 |
| US gallon | litre | 3.7854 | 0.2642 |
| Mass | ounce (oz) | gram | 28.350 | 0.03527 |
| pound (lb) | kg | 0.45359 | 2.2046 |
| short ton (US) | tonne | 0.90718 | 1.1023 |
| long ton (UK) | tonne | 1.0160 | 0.9842 |
| Force | kgf | newton (N) | 9.8067 | 0.10197 |
| lbf | newton (N) | 4.4482 | 0.22481 |
| tonne-force | kN | 9.8067 | 0.10197 |
| Pressure | bar | psi | 14.504 | 0.06895 |
| bar | kPa | 100 | 0.01 |
| kgf/cm2 | bar | 0.98067 | 1.0197 |
| atmosphere | bar | 1.01325 | 0.98692 |
| Stress | N/mm2 | MPa | 1 | 1 |
| ksi | MPa | 6.8948 | 0.14504 |
| kgf/mm2 | MPa | 9.8067 | 0.10197 |
| ton/in2 (UK) | MPa | 15.444 | 0.06475 |
| Torque | ft-lbf | Nm | 1.3558 | 0.73756 |
| in-lbf | Nm | 0.11298 | 8.8507 |
| kgf-m | Nm | 9.8067 | 0.10197 |
| Power | hp (UK / US) | kW | 0.7457 | 1.3410 |
| PS (metric hp) | kW | 0.7355 | 1.3596 |
| Speed | ft/min (sfm) | m/min | 0.3048 | 3.2808 |
| inch/rev (ipr) | mm/rev | 25.4 | 0.03937 |
| mph | km/h | 1.6093 | 0.6214 |
| Flow | US gal/min | litre/min | 3.7854 | 0.2642 |
| cfm (ft3/min) | litre/min | 28.317 | 0.03531 |
| Energy | BTU | kJ | 1.0551 | 0.9478 |
| kWh | MJ | 3.6 | 0.2778 |
Small sizes
| mm | inch | thou |
|---|
| 0.01 | 0.0004 | 0.4 |
| 0.02 | 0.0008 | 0.8 |
| 0.05 | 0.0020 | 2.0 |
| 0.1 | 0.0039 | 3.9 |
| 0.2 | 0.0079 | 7.9 |
| 0.25 | 0.0098 | 9.8 |
| 0.3 | 0.0118 | 11.8 |
| 0.4 | 0.0157 | 15.7 |
| 0.5 | 0.0197 | 19.7 |
| 0.6 | 0.0236 | 23.6 |
| 0.7 | 0.0276 | 27.6 |
| 0.75 | 0.0295 | 29.5 |
| 0.8 | 0.0315 | 31.5 |
| 0.9 | 0.0354 | 35.4 |
Hardness
Hardness conversion (steel, approximate)
| Rockwell | Vickers HV | Brinell HB | Tensile MPa (approx) |
|---|
| 68 HRC | 940 | - | - |
| 66 HRC | 865 | - | - |
| 64 HRC | 800 | 722 | - |
| 62 HRC | 746 | 688 | - |
| 60 HRC | 697 | 654 | - |
| 58 HRC | 653 | 615 | 2330 |
| 56 HRC | 613 | 577 | 2160 |
| 55 HRC | 595 | 560 | 2080 |
| 54 HRC | 577 | 543 | 2010 |
| 52 HRC | 544 | 512 | 1880 |
| 50 HRC | 513 | 481 | 1760 |
| 48 HRC | 484 | 455 | 1640 |
| 46 HRC | 458 | 432 | 1520 |
| 45 HRC | 446 | 421 | 1480 |
| 44 HRC | 434 | 409 | 1430 |
| 42 HRC | 412 | 390 | 1340 |
| 40 HRC | 392 | 371 | 1250 |
| 38 HRC | 372 | 353 | 1180 |
| 36 HRC | 354 | 336 | 1110 |
| 35 HRC | 345 | 327 | 1080 |
| 34 HRC | 336 | 319 | 1050 |
| 32 HRC | 318 | 301 | 1000 |
| 30 HRC | 302 | 286 | 940 |
| 28 HRC | 286 | 271 | 890 |
| 26 HRC | 272 | 258 | 840 |
| 25 HRC | 266 | 253 | 820 |
| 24 HRC | 260 | 247 | 800 |
| 22 HRC | 248 | 237 | 770 |
| 20 HRC | 238 | 226 | 720 |
| 100 HRB | 240 | 240 | 800 |
| 98 HRB | 228 | 228 | 760 |
| 95 HRB | 210 | 210 | 700 |
| 92 HRB | 195 | 195 | 650 |
| 90 HRB | 185 | 185 | 620 |
| 88 HRB | 176 | 176 | 590 |
| 85 HRB | 165 | 163 | 550 |
| 82 HRB | 155 | 153 | 510 |
| 80 HRB | 150 | 146 | 490 |
| 75 HRB | 135 | 133 | 450 |
| 70 HRB | 125 | 121 | 410 |
| 65 HRB | 115 | 111 | 380 |
| 60 HRB | 106 | 105 | 350 |
Hardness scales
| Scale | Indenter and load | Use it for |
|---|
| HRC | 120° diamond cone, 150 kgf | Hardened steel and tool steel, 20 - 68 HRC |
| HRB | 1/16" ball, 100 kgf | Soft steel, brass, aluminium, 20 - 100 HRB |
| HB | 10 mm ball, 3000 kgf (500 kgf soft metals) | Castings, forgings, plate - large average reading |
| HV | 136° diamond pyramid, 1 - 100 kgf | Everything, thin sheet and case-hardened skins (low loads) |
| HRA | 120° diamond cone, 60 kgf | Carbide and very hard thin parts |
Typical hardness
| Material | Typical hardness |
|---|
| Aluminium alloy 6082-T6 | 95 - 100 HB |
| Brass CZ121 (free cutting) | 100 - 160 HV |
| Mild steel (S275, EN1A) | 120 - 160 HB |
| EN8 / 080M40 as rolled | 180 - 220 HB |
| EN19 / 4140 hardened and tempered (T) | 270 - 330 HB (28 - 35 HRC) |
| EN24T / 4340 | 250 - 300 HB |
| Hardox 400 / AR400 plate | 370 - 430 HB |
| Grey cast iron | 180 - 240 HB |
| Spring steel, tempered | 42 - 50 HRC |
| Saw blade, chisel, punch | 52 - 58 HRC |
| Tool steel hardened (O1, D2) | 58 - 62 HRC |
| Files | 62 - 65 HRC |
| HSS drills and taps | 63 - 66 HRC |
| Tungsten carbide | 1300 - 1800 HV (about 88 - 93 HRA) |
Temperature
| °C | °F | °C | °F |
|---|
| -40 | -40 | 350 | 662 |
| -20 | -4 | 400 | 752 |
| -10 | 14 | 450 | 842 |
| 0 | 32 | 500 | 932 |
| 10 | 50 | 550 | 1022 |
| 20 | 68 | 600 | 1112 |
| 30 | 86 | 650 | 1202 |
| 40 | 104 | 700 | 1292 |
| 50 | 122 | 750 | 1382 |
| 60 | 140 | 800 | 1472 |
| 70 | 158 | 850 | 1562 |
| 80 | 176 | 900 | 1652 |
| 90 | 194 | 950 | 1742 |
| 100 | 212 | 1000 | 1832 |
| 120 | 248 | 1100 | 2012 |
| 150 | 302 | 1200 | 2192 |
| 180 | 356 | 1300 | 2372 |
| 200 | 392 | 1400 | 2552 |
| 250 | 482 | 1500 | 2732 |
| 300 | 572 | | |