Power converter

Power units at a glance

Power is the main attribute that shows how fast energy is converted or transferred. Different fields use different units for the same measure—electrical engineers talk in watts and volt-amperes, HVAC technicians use BTU rates and tons of refrigeration, while mechanics most of the time refer to horsepower. Here is a short guide to the units that the converter considers and their equivalents in watts.

SI backbone

• Watt (W), kilowatt (kW), megawatt (MW), gigawatt (GW), terawatt (TW), petawatt (PW) - The SI unit of power; 1 kW = 1,000 W, 1 MW = 1,000,000 W, and so forth. These are the units to be used for general electrical and mechanical power ratings.

Horsepower family

• Horsepower (hp) - Mechanical/imperial hp ≈ 745.7 W, usually referred to engines and motors.
• Metric horsepower (PS) - ≈ 735.5 W, mainly in Europe/automotive specifications.
• Electrical hp (hp(E)) - ≈ 746 W, a formal electrical definition.
• Boiler hp (hp(S)/bhp) - ≈ 9,809.5 W, a unit for steam boilers.
• Hydraulic hp - ≈ mechanical hp, used in fluid power.
• Refrigeration hp - ≈ 3,517 W (about one ton of refrigeration per hp).

Thermal and HVAC

• BTU per hour (BTU/h), BTU/min, BTU/s - British Thermal Units per time; 1 BTU/h ≈ 0.293 W.
• Therm per hour/min/s - 1 therm = 100,000 BTU; mostly seen in gas billing.
• Calories (cal) and kilocalories (kcal) per second/minute/hour - 1 cal ≈ 4.184 J; heat/food consumption, an old background.
• Megacalorie (Mcal) / gigacalorie (Gcal) - Bigger thermal energy units per time, sometimes in industrial heat balance.
• Ton of refrigeration (TR) - 1 TR ≈ 3,516.85 W; the cooling capacity unit.

Mechanical work rates

• Foot-pound per second/minute/hour (ft·lb/s etc.) - Imperial work rate; 1 ft·lb/s ≈ 1.3558 W.
• Kilogram-meter per second/minute (kg·m/s etc.) - Metric work rate; 1 kg·m/s ≈ 9.80665 W.

Electrical and reactive power

• Volt-ampere (VA), kVA, MVA - The total power in AC systems.
• Volt-ampere reactive (var), kvar, Mvar - The reactive power; it is related to reactive current/voltage.
• dBm, dBW - Logarithmic power levels with reference to 1 mW (dBm) or 1 W (dBW), mostly in RF/telecom.
• Coulomb-volt per second, ampere-ohm per second - Simplify to watts; mostly theoretical ones of P = V·I or P = I²·R.

CGS and scientific units

• Erg per second/minute/hour (erg/s etc.) - 1 erg = 1e-7 J; was used in scientific literature of the past.
• Dyne·cm/s, dyne·m/s - CGS power forms; 1 dyne·cm/s = 1e-7 W.

Astronomical and extremes

• Solar luminosity (L☉) - ≈ 3.828e26 W, the Sun's output; good for scaling in astrophysics.
• Bolometric luminosity - The total radiant power over all wavelengths; most of the time it is given in L☉.
• Neutrino luminosity - Occasionally quoted for astrophysical events; can also be standardized to watts.
• Planck power - ≈ 3.63e52 W, a hypothetical upper scale deriving from fundamental constants.

Practical insights for converting power

• Match unit to context: VA/var/kVA/MVA should be used for sizing of an AC circuit; hp or kW only for motors; BTU/h, TR, kcal/h, or therms for heating/cooling loads.
• Mind apparent vs real power: kW is the real power, kVA is the apparent power, and kvar is the reactive power of an AC system. Power factor (kW/kVA) is important for both the equipment sizing and that of the grid-penalty avoiding.
• HP variants differ: Imperial hp (~745.7 W) vs metric hp (~735.5 W) can change the specs by approximately 1-2%. Boiler hp is quite a lot bigger, do not confuse it with mechanical hp.
• Thermal ratings are not electrically convertible: 1-ton air conditioner (~3.5 kW cooling) does not imply that the device is consuming 3.5 kW of electricity; the real input is determined by the efficiency (EER/COP).
• RF power in dBm/dBW: The conversions are logarithmic; +10 dB = 10x power, +3 dB ≈ 2x. 30 dBm = 1 W; 0 dBW = 1 W.
• Great scales: Solar luminosity is mainly used for astrophysical comparisons; Planck power is theoretical—only use it for scaling purposes in thought experiments.
• Check the time bases: BTU/h vs BTU/min vs BTU/s differ by 60 or 3,600 times; the same goes for cal/min and cal/h. Be sure to compare the same time basis.
• Cooling vs heating: TR, BTU/h, and kcal/h are typical HVAC units; therms and kW are usually seen in gas and electric heating bills, respectively. Before comparing costs or efficiencies, make sure you convert values to the same baseline (usually kW).