Power Conversion Calculator
Online calculator and formulas for converting power units
Power Unit Calculator
Power Converter
Select the unit of measurement that you know and enter its value. The calculator supports Watt units, horsepower, and thermal units.
Power Units - Overview
SI System
1 W = 1 J/s (Joule per second)
Kilowatt
1,000 W
≈ 1.341 HP
kWHorsepower
745.7 W
≈ 0.746 kW
HPImportant Conversions
- 1 kW = 1,000 W
- 1 HP (UK) = 745.7 W ≈ 0.746 kW
- 1 PS (metric) = 735.5 W ≈ 0.735 kW
- 1 kW ≈ 1.341 HP ≈ 1.360 PS
- 1 cal/s = 4.187 W
Watt Units (SI)
The Watt (W) is the SI unit for power:
- 1 mW (milliwatt) = 10⁻³ W
- 1 W (watt) = 1 J/s = base unit
- 1 kW (kilowatt) = 1,000 W
- 1 MW (megawatt) = 1,000,000 W
- Named after James Watt
Horsepower
Horsepower units for engines and motors:
- HP (UK/Imperial): 745.7 W
Mechanical horsepower - PS (metric): 735.5 W
Pferdestärke (Germany) - Difference: HP is ~1.4% more than PS
- Used mainly for cars, engines
Thermal Units
Units based on heat energy:
- cal/s (calorie per second): 4.187 W
Heat energy transfer - kcal/s (kilocalorie per second): 4,187 W
Large scale heating - BTU/s (British Thermal Unit per second): 1,055 W
HVAC systems
Power vs. Energy
Power is the rate of energy transfer (Watt = Joule/second). Energy is the capacity to do work (Joule, kWh). Example: A 100W light bulb uses 100 Joules per second, or 0.1 kWh per hour.
Formulas for Converting Power Units
kW ↔ Horsepower
Metric Horsepower (PS)
The power of 1 metric horsepower corresponds to 735.49875 watts.
\(W = PS \cdot 735.49875\)
W → PS:
\(\displaystyle PS=\frac{W}{735.49875}\)
\(W = 100 \cdot 735.49875 = 73,549.875\text{ W}\)
\(kW = 73,549.875 \div 1000 = 73.55\text{ kW}\)
British Horsepower (HP)
The power of 1 horsepower corresponds to 745.70 watts.
\(W = HP \cdot 745.7\)
W → HP:
\(\displaystyle HP=\frac{W}{745.7}\)
\(W = 75 \cdot 1000 = 75,000\text{ W}\)
\(HP = 75,000 \div 745.7 = 100.58\text{ HP}\)
kW ↔ Thermal Units
Calorie per Second
The power of 1 calorie per second corresponds to 4.1868 watts.
\(W = \frac{cal}{s} \cdot 4.1868\)
W → cal/s:
\(\displaystyle \frac{cal}{s}=\frac{W}{4.1868}\)
\(W = 1000\text{ W}\)
\(cal/s = 1000 \div 4.1868 = 238.85\text{ cal/s}\)
BTU per Second
The power of 1 BTU per second corresponds to 1055.05585262 watts.
\(W = \frac{BTU}{s} \cdot 1055.05585262\)
W → BTU/s:
\(\displaystyle \frac{BTU}{s}=\frac{W}{1055.05585262}\)
\(W = 10,000\text{ W}\)
\(BTU/s = 10,000 \div 1055.06 = 9.48\text{ BTU/s}\)
Comparison Table
| Unit | Symbol | Equivalent in Watts | Category |
|---|---|---|---|
| Watt | W | 1 | SI Unit |
| Kilowatt | kW | 1,000 | SI Unit |
| Megawatt | MW | 1,000,000 | SI Unit |
| Horsepower (UK) | HP | 745.7 | Horsepower |
| Horsepower (metric) | PS | 735.5 | Horsepower |
| Calorie per second | cal/s | 4.187 | Thermal |
| BTU per second | BTU/s | 1,055.06 | Thermal |
Practical Applications
Everyday Use:
- Light bulbs: 5-100 W
- Hair dryer: 1,000-2,000 W
- Microwave: 600-1,200 W
- Washing machine: 2,000-2,500 W
- Electric car: 50-200 kW
Industrial Use:
- Car engine: 50-500 HP (37-373 kW)
- Wind turbine: 2-5 MW
- Power plant: 500-1,500 MW
- HVAC systems: BTU/s or kW
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