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Units Converter

Convert a value across 18 categories — length, mass, pressure, energy, power, flow, and the heat-transfer units (conductivity, heat flux, HTC, specific heat, viscosity).

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One bar is not one atmosphere: 1 atm = 1.01325 bar. A 1.3% slip that goes unnoticed until it meets a vacuum spec or a combustion calculation.

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Units Converter

Converts a numeric value between compatible engineering units across 18 categories. The category taxonomy mirrors unitconverters.net; conversion factors are SI/NIST-exact (International Table calorie/BTU convention).

Pick a Category first — the From and To lists then show only the units in that category.

Supported categories

CategoryUnits
Lengthm, km, dm, cm, mm, µm, mi, yd, ft, in
Aream², km², cm², mm², ha, mi², yd², ft², in², acre
Volumem³, L, mL, cm³, ft³, in³, gal (US), gal (UK), qt (US), pt (US), fl oz (US), bbl
TemperatureK, °C, °F, °R
Mass / Weightkg, g, mg, t, lb, oz, slug, gr
PressurePa, kPa, MPa, bar, mbar, atm, psi, torr, mmHg, inHg, mmH₂O
EnergyJ, kJ, MJ, Wh, kWh, cal, kcal, BTU (IT), ft·lbf, therm (US), eV
PowerW, kW, MW, hp, hp, BTU/h, ft·lbf/s, cal/s (IT)
ForceN, kN, dyn, kgf, lbf, ozf, pdl
Speedm/s, km/h, ft/s, mph, knot, ft/min
Volumetric flowm³/s, m³/h, L/s, L/min, ft³/s, ft³/min, gal/min (US gpm)
Densitykg/m³, g/cm³, kg/L, lb/ft³, lb/in³, slug/ft³
Thermal conductivityW/(m·K), W/(cm·K), kcal/(h·m·°C), cal/(s·cm·°C), BTU/(h·ft·°F), BTU·in/(h·ft²·°F)
Heat flux densityW/m², kW/m², W/cm², cal/(s·cm²), kcal/(h·m²), BTU/(h·ft²)
Heat-transfer coefficientW/(m²·K), W/(cm²·K), kcal/(h·m²·°C), cal/(s·cm²·°C), BTU/(h·ft²·°F)
Specific heat capacityJ/(kg·K), kJ/(kg·K), cal/(g·°C) (IT), kcal/(kg·°C) (IT), BTU/(lb·°F) (IT)
Dynamic viscosityPa·s, mPa·s, P, cP, lbf·s/ft², lb/(ft·s)
Kinematic viscositym²/s, cm²/s, St, cSt, ft²/s, m²/h

Affine factor-map conversion

Every unit maps to its category's base unit by an affine relation:

base=xf+o,y=fto(xffrom+ofrom)oto

The offset o is zero for all categories except temperature, so for ratio units this reduces to y=xffrom/fto.

Example: 1ft=0.3048m.

Temperature

TC=1.8TF32,TK=TC+273.15

Rankine (°R) is the absolute Fahrenheit scale: TR=1.8TK.

Heat-transfer units

The thermal families use the International Table calorie (cal = 4.1868 J, kcal = 4186.8 J, BTU = 1055.05585 J), giving the standard published figures — e.g. 1kcal/(h⋅m⋅°C)=1.163W/(m⋅K) and 1BTU/(lb⋅°F)=4186.8J/(kg⋅K).

Usage note

Selecting From/To units from different categories produces a dimension-mismatch error.

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Frequently asked questions

Convert a value across 18 categories — length, mass, pressure, energy, power, flow, and the heat-transfer units (conductivity, heat flux, HTC, specific heat, viscosity). Enter your inputs and press Calculate — the worked solution shows every step of the method with your numbers substituted in.

Factors are SI/NIST-exact where an exact definition exists (inch, pound, bar) and follow the International Table convention for the BTU and calorie. Temperature conversions handle the °C/°F/K offsets exactly rather than as pure multipliers.

Units only interconvert within a category — pressure to pressure, energy to energy. The category selector enforces this, which makes dimensionally invalid conversions impossible rather than silently wrong.