12 categories · 90+ engineering units · instant conversion
All conversions use SI base units as intermediate · Temperature uses °C as pivot
Unit Converter — 12 Engineering Categories, 90+ Units (SI / Imperial)
The MechanixCalc Unit Converter handles the full set of physical quantities that arise in mechanical engineering practice: length, area, volume, mass, force, pressure, torque, power, energy, linear velocity, angular velocity and temperature — 12 categories covering 90+ units. Enter a value, choose your source and target units, and the result appears immediately. The all-equivalents broadcast panel simultaneously shows the entered quantity in every unit of the active category, so you can scan the entire range without extra clicks.
Conversion factors follow the SI definitions in the BIPM SI Brochure (9th edition) and the NIST SP 811 guide for US customary units; temperature uses the ITS-90 affine relations (°C as pivot, exact offsets for K, °F and °R). The tool also includes a complete 24-prefix SI prefix reference (Yotta → Yocto) and a conversion-history log — making it a daily-use companion for engineers working across metric and imperial standards.
What this calculator does
- 12 engineering unit categories: length, area, volume, mass, force, pressure, torque, power, energy, linear velocity, angular velocity and temperature
- 90+ engineering units with exact SI-definition conversion factors (BIPM / NIST SP 811)
- All-equivalents broadcast panel — shows the entered value in every unit of the active category simultaneously
- Common-conversions quick-reference card per category (e.g. MPa ↔ psi, kW ↔ hp, rpm ↔ rad/s)
- Temperature: correct affine (offset + scale) conversions for °C, K, °F and °R using ITS-90 relations
- SI prefix reference table — all 24 prefixes Yotta (10²⁴) to Yocto (10⁻²⁴) with symbols and common examples
- Conversion history log with copy-to-clipboard for the last 15 conversions
Method & formulas
SI-pivot conversion method
Every non-temperature unit is stored with a single multiplier that converts it to the SI base unit for its quantity (e.g. metre for length, pascal for pressure, newton for force). To convert between any two units, the tool multiplies the input value by the source-unit's toSI factor and then by the target-unit's fromSI factor (the reciprocal of its toSI). This two-step pivot through SI avoids accumulating round-off from chained unit-to-unit tables and ensures that any pair of units in a category can be converted consistently from a single set of stored constants.
y = x · toSI_A · fromSI_B where fromSI_B = 1 / toSI_Bwhere x = input value in unit A; toSI_A = factor converting unit A to the SI base unit; toSI_B = factor converting unit B to the SI base unit; y = result in unit B
Temperature: affine (offset + scale) conversion
Temperature cannot be converted by a simple multiplier because its scales have different zero points. The tool uses Celsius (°C) as the intermediate pivot. Any input temperature is first converted to °C, then from °C to the target scale, using the exact ITS-90 relations: K = °C + 273.15; °F = °C × 9/5 + 32; °R = (°C + 273.15) × 9/5.
T_K = T_C + 273.15where T_C = temperature in Celsius; T_K = temperature in Kelvin (ITS-90 definition, exact)
T_F = T_C × (9/5) + 32where T_C = temperature in Celsius; T_F = temperature in Fahrenheit
Angular velocity conversion
Angular velocity is the quantity most frequently confused in rotating-machinery engineering. The SI unit is radian per second (rad/s), but speeds are reported in revolutions per minute (rpm) on motor nameplates and datasheets. The exact conversion is ω [rad/s] = n [rpm] × 2π / 60. The tool stores this factor directly (toSI = 2π/60 ≈ 0.104720 rad·s⁻¹·rpm⁻¹), so no intermediate rounding is introduced.
ω = n · 2π / 60where ω = angular velocity (rad/s); n = rotational speed (rpm); 2π = one full revolution in radians; 60 = seconds per minute
Worked example
Convert a motor speed of 1500 rpm to radians per second — a common step when computing centripetal acceleration or shaft power from torque in SI units.
Given
- Motor speed n1500 rpm
Result
- Angular velocity ω157.08 rad/s
- Identify the conversion factor: 1 rpm = 2π / 60 rad/s ≈ 0.104720 rad/s.
- Multiply: ω = 1500 × 0.104720 = 157.08 rad/s.
- Cross-check via the definition: 1500 rpm means 1500 / 60 = 25 revolutions per second. One revolution = 2π radians, so ω = 25 × 2π = 25 × 6.28318 = 157.08 rad/s. ✓
This is an illustrative single-step example. The converter handles all 12 categories identically — enter your value, select units, read the result.
Frequently asked questions
Which standard does the Unit Converter use?
Conversion factors follow the BIPM SI Brochure (9th edition, 2019) for SI-defined units and NIST SP 811 for US customary and other legacy units. Temperature conversions use the ITS-90 affine relations (°C as pivot). There is no single governing standard for a general-purpose converter — these are the authoritative international references for the values used.
Is the Unit Converter free?
Yes — the Unit Converter is permanently free with no sign-up required. You can also use it during a free 30-minute preview session that unlocks every calculator on the platform. A free 14-day account trial (no credit card) gives access to all tools; saved calculations and branded PDF reports are part of a paid plan.
How accurate are the conversion factors?
All multiplicative conversion factors are stored at full IEEE-754 double precision (15–16 significant figures) and derived from SI definitions or NIST SP 811 values, which are exact or specified to more digits than double precision can represent. Results are displayed to 6 significant figures, which is appropriate for engineering work. Temperature conversions use the exact ITS-90 offsets (273.15 K exactly, 32 °F exactly).
What engineering categories are covered?
The converter covers 12 categories: length (11 units including μm and nautical miles), area, volume (including Oil Barrel and UK/US gallons), mass (including slug and grain), force (including kgf, lbf and dyne), pressure (including bar, atm, psi, ksi and N/mm²), torque (including lbf·ft, lbf·in and kgf·m), power (metric and imperial horsepower, BTU/h), energy (kWh, BTU, kcal), linear velocity (m/s, km/h, mph, knot), angular velocity (rpm, rad/s, deg/s, rev/s) and temperature (°C, K, °F, °R). New categories may be added in future updates.
Why does temperature conversion work differently from the other categories?
All other physical quantities have ratio scales — zero means 'none of the quantity' and a pure multiplication converts between units. Temperature scales (except Kelvin) are affine: they have different zero points, so conversion requires both a scale factor and an offset. The tool uses °C as an intermediate pivot, applying the exact ITS-90 relation for each target scale, so it correctly handles cases like 0 °C → 32 °F or 0 °C → 273.15 K.
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