Engineering Unit Converter
Bidirectional engineering conversions across every MEP unit category, with PDF export.
Free · no sign-in requiredPurpose
Convert between SI and Inch-Pound units when reading a foreign specification, checking a vendor submission or transferring figures between a design tool and a drawing set.
Inputs required
A value, the category it belongs to, and the source and target units. Conversions are bidirectional, so swapping the units re-converts immediately.
Standards followed
SI definitions follow ISO 80000. Airflow, pressure, capacity and heat-transfer conversions use the factors published in the ASHRAE Handbook — Fundamentals unit conversion tables.
All conversions
Engineering reference & methodology
Categories covered
Airflow (m³/s, m³/h, L/s, CFM), pressure (Pa, kPa, bar, mm water gauge, inches water gauge, psi), power and capacity (W, kW, TR, BTU/h, kcal/h), temperature (°C, K, °F), liquid flow (L/s, L/min, m³/h, GPM), velocity, length, area, volume, mass, mass flow, energy, thermal conductivity and heat-transfer coefficient (W/m²·K, BTU/h·ft²·°F).
Absolute values versus differences
Temperature needs care. An absolute temperature conversion applies the offset (°F = °C × 1.8 + 32), while a temperature difference does not (1 K difference equals 1 °C difference equals 1.8 °F difference). Use the temperature category for absolute conditions and treat design deltas as differences, or a 10 °C delta becomes an incorrect 50 °F.
Refrigeration capacity
One ton of refrigeration is 3.51685 kW, equal to 12 000 BTU/h — the heat rate that freezes one short ton of ice in 24 hours. It is a rate of heat removal, not a mass. Converting a chiller duty to TR does not change the flow or temperature difference that produced it.
Pressure reference conditions
Head expressed in millimetres or inches of water assumes water at about 4 °C and standard gravity; 1 mm water gauge is 9.80665 Pa. For hot water or glycol solutions, correct for the actual fluid density before treating a head figure as a pressure. Air-side pressures in HVAC are gauge values referenced to the surrounding space, not absolute.
Air density assumption
Volumetric airflow is not conserved when density changes. A duct carrying 1 m³/s at sea level carries the same volume but less mass at altitude or at high temperature. Where a calculation depends on mass flow — heating and cooling capacity, for example — convert to mass flow using the actual air density rather than the standard 1.2 kg/m³ at 20 °C and 101.325 kPa.
Results are preliminary design guidance. Verify every value against the edition of each standard adopted by your project or authority having jurisdiction, and against manufacturer performance data, before using it in design or procurement.
Psychrometrics, cooling loads, duct & pipe sizing, pumps, cleanrooms, electrical design and PDF reports.