Type into any unit and everything else updates.
Nine categories: length, area, volume, mass, flow rate, pressure, power, energy, temperature. Pin combinations for later use or export.
For force conversions (kgf, lbf, N) use a dedicated tool. For design guidance only. Always verify against the originating standard.
About this engineering unit converter
This free engineering unit converter handles the conversions UK building-services engineers, M&E estimators and site teams reach for every day, across nine domains: length, area, volume, mass, flow rate, pressure, power, energy and temperature. Type a value into any unit and every other field in that category updates live. Pin the combinations you use most and export them to CSV. The figures mirror the verified Ensign Toolbox engine exactly.
How the conversions work
Each unit carries an exact multiplicative factor to its domain’s SI base (the metre, kilogram, pascal, watt, joule, and so on). A conversion is two steps: multiply the input by the source unit’s factor to reach the base, then divide by the target unit’s factor, so any unit maps to any other and the result is exactly reversible. The factors are the values defined in NIST SP 811 (2008 ed.), Appendix B, for example 1 ft = 0.3048 m and 1 BTU = 1055.05585262 J. Temperature is the exception: with different zero points, it is an affine map to kelvin (a slope and offset per unit, per ISO 80000-5) rather than a single factor.
Frequently asked questions
Which categories and units are covered?
Nine categories, each with the metric and imperial/US units common in UK building services: miles, US and imperial gallons, psi, mmHg, metres of water, horsepower and metric horsepower (PS), BTU and calories, and the Celsius, Fahrenheit, kelvin and Rankine temperature scales.
Why convert through an SI base unit?
Routing every unit through one base means a single factor per unit converts any unit to any other in that category, exactly reversibly. It also keeps the arithmetic identical to the published standard, where the factors are defined against the SI base.
Are the conversion factors exact?
Where the standard defines a factor exactly, such as the international foot (0.3048 m), the avoirdupois pound (0.45359237 kg) or the IT British thermal unit (1055.05585262 J). The calculator uses that exact value from NIST SP 811. Results are indicative; check them against the originating standard for safety-critical work.