Unit converter
Converts structural quantities between US customary and SI units with exact factors. Choose the quantity, enter the value, and pick the unit to convert from and to; the results also list the value in every other unit of the quantity.
Inputs of the unit converter #
- Quantity: length, area, force, moment, stress and pressure, line load, area load, unit weight (force per volume: pcf, kN/m³), density (mass per volume: lb/ft³, kg/m³), speed, moment of inertia, section modulus, temperature.
- Value and the From and To units of that quantity.
Unit weight and density are different quantities: a unit weight of 1 pcf is a density of 1 lb/ft³ only under standard gravity, so they are kept apart.
Results and checks of the unit converter #
| Row | Basis |
|---|---|
| Conversion basis | NIST SP 811 (2008) Appendix B: 1 in = 0.0254 m, 1 lb = 0.45359237 kg and gn = 9.80665 m/s² are exact, so 1 lbf = 4.4482216152605 N, 1 kgf = 9.80665 N; 1 mi = 5280 ft, 1 acre = 43,560 ft², 1 knot = 1852 m/h; the step shows both units in the SI base unit and the factor |
| Temperature | Through kelvin: 0 °C = 273.15 K, 0 °F = 459.67 °R, 1 °F = 5/9 K (an offset, not a factor) |
| Round trip | The result converts back to the entered value |
| Value is physical | A temperature below absolute zero is NOT FEASIBLE |
The ton is the short ton (2000 lbf); the tonne-force is the metric 1000 kgf.
Limitations #
- Results are shown to six significant figures; the factors are exact to double precision.
- Mass, energy, power and angle are not offered.
Verification examples #
Exact values from the NIST SP 811 definitions (tests/test_verify_unit_converter.py), matched to 1 part in 10⁹:
| Example | Conversion | Exact | ILX Calcs |
|---|---|---|---|
| UC-1 | 1 ft | 304.8 mm | 304.8 |
| UC-2 | 1 kip | 4.4482216152605 kN | 4.44822 |
| UC-3 | 1 ksi | 6.894757293168 MPa | 6.89476 |
| UC-4 | 1 psf | 47.88025898034 Pa | 47.8803 |
| UC-5 | 1 kip-ft | 1.3558179483314 kN-m | 1.35582 |
| UC-6 | 1 klf | 14.593902937206 kN/m | 14.5939 |
| UC-7 | 1 pcf | 157.0874638 N/m³ | 157.087 |
| UC-8 | 1 in⁴ | 416,231.4256 mm⁴ | 416,231 |
| UC-9 | 100 mph | 44.704 m/s | 44.704 |
| UC-10, UC-11 | 32 °F, 212 °F | 0 °C, 100 °C | 0, 100 |
| UC-12 | 1 lb/ft³ (mass) | 16.01846337 kg/m³ | 16.0185 |
Published factors of NIST SP 811 (2008), Appendix B.8 (seven significant digits; matched to 1 part in 10⁶; PDF page of the free NIST document in brackets):
| Example | Conversion | NIST SP 811 | ILX Calcs |
|---|---|---|---|
| SP811-1, -2 | 1 kip; 1 ksi | 4.448 222 kN [63]; 6.894 757 MPa [63] | same |
| SP811-3, -4 | 1 psi; 1 psf | 6.894 757 kPa [65]; 47.880 26 Pa [65] | same |
| SP811-5, -6, -7 | 1 lbf·ft; 1 lbf·in; 1 kgf·m | 1.355 818; 0.112 984 8; 9.806 65 N·m [63, 65] | same |
| SP811-8, -9 | 1 lbf/ft; 1 lbf/in | 14.593 90; 175.126 8 N/m [65] | same |
| SP811-10, -11 | 1 ton-force (2000 lbf); 1 kgf | 8.896 443 kN [67]; 9.806 65 N [63] | same |
| SP811-12, -13 | 1 in⁴; 1 ft⁴ | 4.162 314 × 10⁻⁷; 8.630 975 × 10⁻³ m⁴ [61, 62] | same |
| SP811-14, -15 | 1 in²; 1 ft² | 6.4516 × 10⁻⁴; 9.290 304 × 10⁻² m² [66, 67] | same |
| SP811-16 to -19 | 1 mile; 1 yd; 1 mph; 1 ft/s | 1.609 344 km; 0.9144 m; 1.609 344 km/h; 0.3048 m/s [61, 64, 68] | same |
| SP811-20 | 1 lb/ft³ (mass) | 16.018 46 kg/m³ [66] | same |
| SP811-21, -22 | 1 atm; 1 bar | 101.325 kPa; 100 kPa [57] | same |