Power Converter

Convert between watts, kilowatts, horsepower, BTU/hr, and more power units instantly. Essential for electrical and mechanical applications.

Quick Facts

1 Horsepower (Mech)
745.7 Watts
Common in automotive
1 Kilowatt
1,000 Watts
Standard metric unit
1 BTU/hour
0.293 Watts
Used in HVAC systems
1 Ton of Cooling
12,000 BTU/hr
Air conditioning unit

Conversion Result

1 Watts
0.001341 Horsepower (Mechanical)

Quick Reference

  • 1 W = 0.001 kW
  • 1 W = 0.00134 HP (mechanical)
  • 1 W = 3.412 BTU/hr

Real-World Examples

  • LED light bulb: 8-15W
  • Laptop charger: 45-90W
  • Smartphone charger: 5-20W

What is Power?

Power is the rate at which energy is transferred, converted, or consumed over time. Measured in watts (W) in the International System of Units, power indicates how quickly work is performed. One watt equals one joule of energy transferred per second.

Power conversions are essential in electrical engineering, mechanical engineering, HVAC design, motor specification, and energy consumption analysis. Understanding different power units helps engineers select appropriate equipment, calculate energy costs, and design efficient systems.

Common Power Units Explained

Watt (W)

The SI unit of power, defined as one joule per second. Named after James Watt, the Scottish inventor who improved the steam engine.

  • 1 Watt: Very small, about the power of a small LED bulb
  • 60 Watts: Traditional incandescent light bulb
  • 1,000 Watts (1 kW): Microwave oven, hair dryer
  • 1,000,000 Watts (1 MW): Large industrial motors, small power plant

Horsepower (hp)

A unit of power originally defined by James Watt to compare steam engine output with draft horses. Multiple definitions exist:

Types of Horsepower

  • Mechanical (US): 745.7 W - most common in automotive
  • Metric (PS): 735.5 W - used in Europe
  • Electrical: 746 W - defined for electrical motors
  • Boiler: 9,810 W - for steam boilers

BTU per Hour (BTU/hr)

British Thermal Unit per hour, commonly used in HVAC systems. One BTU is the energy needed to raise one pound of water by one degree Fahrenheit.

  • 1 BTU/hr = 0.293 Watts
  • HVAC systems rated in thousands of BTU/hr
  • 12,000 BTU/hr = 1 ton of cooling
  • Natural gas appliances rated in BTU/hr

Power Conversion Table

Unit Watts Equivalent Common Use
1 Watt 1 W Small electronics
1 Kilowatt 1,000 W Household appliances
1 Horsepower (mech) 745.7 W Motors, engines
1 BTU/hr 0.293 W HVAC systems
1 Ton of Cooling 3,516 W Air conditioning

Practical Applications

Electrical Systems

Electrical power calculations use watts to determine circuit breaker sizing, wire gauge selection, and energy consumption. The relationship P = VI (power equals voltage times current) is fundamental to electrical engineering.

Motor Selection

Motors are specified in horsepower (US) or kilowatts (metric). Converting between these units ensures proper motor sizing for pumps, compressors, conveyors, and industrial machinery.

HVAC Design

Heating and cooling systems use BTU/hr or tons of cooling. A 3-ton AC unit provides 36,000 BTU/hr of cooling (about 10.5 kW). Converting between units helps compare equipment efficiency.

Energy Cost Calculation

Electricity is billed in kilowatt-hours (kWh), the amount of energy consumed by a 1-kW device running for 1 hour. A 100W bulb running 10 hours uses 1 kWh.

Power vs. Energy

Power and energy are related but distinct concepts:

Key Differences

  • Power: Rate of energy transfer (watts)
  • Energy: Total amount of work done (joules or watt-hours)
  • Analogy: Power is like speed (mph), energy is like distance (miles)
  • Formula: Energy = Power x Time

Common Conversions

Watts to Horsepower

Divide watts by 745.7 for mechanical horsepower:

  • 1,000 W / 745.7 = 1.34 hp
  • 5,000 W / 745.7 = 6.7 hp
  • 100 hp x 745.7 = 74,570 W (74.57 kW)

BTU/hr to Watts

Multiply BTU/hr by 0.293:

  • 12,000 BTU/hr x 0.293 = 3,516 W (3.5 kW)
  • 24,000 BTU/hr = 7,032 W (7 kW) - about 2 tons AC
  • 40,000 BTU/hr furnace = 11,720 W input

Kilowatts to Tons of Cooling

One ton of cooling equals 3.517 kW:

  • 3 ton AC = 10.55 kW cooling capacity
  • 18,000 BTU mini-split = 1.5 tons = 5.3 kW

Efficiency Considerations

When converting power units, remember that efficiency affects actual output:

  • Electric motors: 85-95% efficient (1 hp motor draws more than 746W)
  • Internal combustion engines: 20-30% efficient
  • LED lights: Convert 20-30% of power to light
  • Incandescent bulbs: Only 5% efficient

Frequently Asked Questions

How many watts is 1 horsepower?

Mechanical horsepower equals 745.7 watts. Metric horsepower (used in Europe) equals 735.5 watts. Electrical horsepower is defined as exactly 746 watts.

Why are different horsepower standards used?

Historical reasons. James Watt defined horsepower based on observations of draft horses. Different industries and regions adopted slightly different definitions. Modern engineering typically uses watts for precision.

How do I convert AC tonnage to watts?

One ton of air conditioning equals 12,000 BTU/hr or 3,517 watts. So a 3-ton AC unit provides 10,551 watts (10.55 kW) of cooling capacity.

What's the difference between power input and output?

Input power is electrical power consumed. Output power is mechanical work performed. The difference is losses (heat, friction, noise). Efficiency = Output / Input.

How do I calculate electricity costs from watts?

Convert watts to kilowatts (divide by 1,000), multiply by hours of operation to get kWh, then multiply by your electricity rate ($/kWh). Example: 1,500W heater x 8 hours / 1,000 x $0.12/kWh = $1.44.

Can I use a higher horsepower motor than specified?

Generally yes, but consider: 1) Oversized motors run less efficiently at low loads, 2) Higher inrush current may trip breakers, 3) May require larger wiring and breakers, 4) Cost more to purchase and operate.