How many watts are in 1 horsepower?

1 mechanical (UK) horsepower = 745.7 watts. 1 metric horsepower (PS) = 735.5 watts. 1 electrical horsepower = 746 watts exactly. For rough estimates, 1 HP is approximately 750 watts or three-quarters of a kilowatt.

Why do car engines use horsepower instead of watts?

Historical convention from James Watt who marketed steam engines in horsepower so buyers could compare to horses. The term stuck in automotive culture. European manufacturers increasingly use kW alongside HP/PS.

Why do solar panels use kW?

Solar panels use kilowatts peak (kWp) to represent maximum power output under standard test conditions. A 5 kWp system means it can produce up to 5000 watts at peak sunlight. Actual output varies by weather and orientation.

How do I calculate my electricity bill from watts?

Energy (kWh) = Power (watts) divided by 1000 multiplied by Hours used. Example: A 2000W heater for 3 hours daily for 30 days = 180 kWh. At Rs 8 per unit, that costs Rs 1440 per month.

What does 1 ton AC mean in watts?

1 ton of refrigeration = 12000 BTU/hour = 3517 watts of cooling capacity. However, a 5-star inverter 1-ton AC only consumes 700-900W of electricity due to its efficiency.

What is boiler horsepower?

1 boiler HP = 9812.5 watts (about 13.2 mechanical HP). Originally defined as the power to evaporate 34.5 pounds of water per hour. Used exclusively for steam boiler specifications.

How many solar panels do I need for 1 kW?

For 1 kW capacity, you need 2-3 modern panels (400-500W each). A 1 kW system produces about 4-5 kWh per day in India. Space required is approximately 60-80 sq ft per kW.

What is the difference between HP and PS?

HP (mechanical) = 745.7W, PS (metric) = 735.5W. The difference is about 1.4%. PS is used in European and Japanese car specifications. A car rated at 200 PS equals approximately 197 HP.

Can I run a 2000W appliance on a 1 kW inverter?

No. A 1 kW inverter handles loads up to approximately 800W after efficiency losses. For a 2000W appliance, you need at least a 2.5 kVA inverter. Always add a 20-30% safety margin.

Power Converter

Convert between watts, kilowatts, horsepower, megawatts, BTU/hour, and 21 other power units

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What Is Power?

Power is the rate at which energy is transferred, used, or transformed. In physics, it measures how quickly work is done or energy is converted from one form to another. A device with higher power output performs the same amount of work in less time.

The SI unit of power is the watt (W), named after James Watt. One watt equals one joule of energy transferred per second (1 W = 1 J/s). Power is fundamentally different from energy — power is the rate of energy use, while energy is the total amount consumed over time.

Key Formula: Power (P) = Energy (E) ÷ Time (t) = Work (W) ÷ Time (t)
Electrical Power: P = Voltage (V) × Current (I)
Mechanical Power: P = Force (F) × Velocity (v)

Why Power Conversion Matters

Different industries and countries use different power units. Automotive engineers work with horsepower, HVAC technicians use BTU/hour, electrical engineers use watts and kilowatts, while power plant operators think in megawatts and gigawatts. Converting between these units is essential for international collaboration, equipment specification comparison, and regulatory compliance.

Power Units Explained

Watt (W)

The SI base unit of power. One watt equals one joule per second. Used universally for electrical devices, lighting, and electronics. A typical LED bulb uses 9W, a laptop charger draws 65W.

Kilowatt (kW)

Equal to 1,000 watts. The standard unit for household appliances, solar panels, and small motors. A typical home consumes 1–3 kW on average. Air conditioners are rated in kW (1 ton ≈ 3.5 kW).

Megawatt (MW)

Equal to 1,000,000 watts or 1,000 kW. Used for power plants, large industrial facilities, and wind farms. A single wind turbine produces 2–5 MW. A coal plant generates 500–1,000 MW.

Gigawatt (GW)

Equal to 1,000 MW or 1 billion watts. Used for national power grids and total generation capacity. India's total installed capacity is approximately 430 GW (2025).

Horsepower — Mechanical (HP)

Equal to 745.7 watts. Defined by James Watt based on the power of a draft horse. Used for car engines, industrial motors, and pumps. A typical car engine produces 100–300 HP.

Metric Horsepower (PS)

Equal to 735.5 watts. Used in Europe and Japan (PS = Pferdestärke in German). Slightly less than mechanical HP. European car specs use PS rather than HP.

BTU/hour

British Thermal Unit per hour. Equal to 0.293 watts. The standard unit for HVAC systems, heating capacity, and cooling in North America. An AC's 12,000 BTU/hr = 1 ton = 3.5 kW.

Calorie/second

Equal to 4.184 watts. Used in thermochemistry and food science contexts. Represents heat flow rate in calorimetry experiments.

Milliwatt (mW)

Equal to 0.001 watts. Used for low-power electronics like sensors, Bluetooth devices, and microcontrollers. A typical Bluetooth radio transmits at 1–100 mW.

Power Conversion Formulas & Quick Reference

From	To	Formula	Example
Watts	Kilowatts	Divide by 1,000	1,500 W = 1.5 kW
Kilowatts	Watts	Multiply by 1,000	2.5 kW = 2,500 W
Watts	Horsepower (mech.)	Divide by 745.7	5,000 W = 6.71 HP
Horsepower	Watts	Multiply by 745.7	3 HP = 2,237 W
Kilowatts	Horsepower	Multiply by 1.341	100 kW = 134.1 HP
Horsepower	Kilowatts	Multiply by 0.7457	200 HP = 149.1 kW
Watts	BTU/hour	Multiply by 3.412	1,000 W = 3,412 BTU/hr
BTU/hour	Watts	Multiply by 0.293	10,000 BTU/hr = 2,930 W
Kilowatts	Megawatts	Divide by 1,000	5,000 kW = 5 MW
Megawatts	Gigawatts	Divide by 1,000	1,200 MW = 1.2 GW
HP (metric)	HP (mechanical)	Multiply by 0.9863	100 PS = 98.63 HP
Boiler HP	Watts	Multiply by 9,812.5	1 BHP = 9,812.5 W

Worked Examples

Example 1: A 2 HP water pump — how many watts?
2 HP × 745.7 = 1,491.4 W ≈ 1.5 kW
This helps determine the circuit breaker size needed.

Example 2: A 12,000 BTU/hr AC — how many kW?
12,000 × 0.293 = 3,516 W = 3.52 kW
This is a 1-ton AC, common for bedrooms up to 150 sq ft.

Example 3: A 150 HP car engine — how many kW?
150 × 0.7457 = 111.86 kW
European car specs would list this as ~112 kW or 152 PS.

Example 4: A 5 kW solar system — annual energy output?
5 kW × 4.5 sun-hours × 365 = 8,212 kWh/year
Note: kW is power (rate), kWh is energy (total).

Real-World Power Consumption Examples

Understanding how much power everyday devices use helps put the units in context:

Device / System	Typical Power	In kW	In HP
LED Bulb	9 W	0.009 kW	0.012 HP
Smartphone Charger	5–20 W	0.005–0.02 kW	0.007–0.027 HP
Ceiling Fan	70 W	0.07 kW	0.094 HP
Laptop Charger	45–65 W	0.045–0.065 kW	0.06–0.087 HP
Desktop Computer	200–500 W	0.2–0.5 kW	0.27–0.67 HP
Washing Machine	500 W	0.5 kW	0.67 HP
Microwave Oven	1,000–1,200 W	1.0–1.2 kW	1.34–1.61 HP
Electric Iron	1,000–2,000 W	1.0–2.0 kW	1.34–2.68 HP
Electric Kettle	1,500–2,000 W	1.5–2.0 kW	2.01–2.68 HP
Air Conditioner (1 Ton)	3,500 W	3.5 kW	4.69 HP
Electric Car Motor	100,000–300,000 W	100–300 kW	134–402 HP
Wind Turbine (large)	2,000,000–5,000,000 W	2,000–5,000 kW	2,682–6,705 HP
Nuclear Power Plant	1,000,000,000 W	1,000,000 kW	1 GW

Complete Power Conversion Table

Quick reference for converting between the most common power units (values rounded):

Unit	Watt (W)	Kilowatt (kW)	Horsepower (HP)	BTU/hour	Megawatt (MW)
1 Watt	1	0.001	0.00134	3.412	0.000001
1 Kilowatt	1,000	1	1.341	3,412	0.001
1 Horsepower	745.7	0.7457	1	2,544	0.000746
1 BTU/hour	0.293	0.000293	0.000393	1	0.000000293
1 Megawatt	1,000,000	1,000	1,341	3,412,000	1
1 Metric HP (PS)	735.5	0.7355	0.9863	2,510	0.000736
1 Boiler HP	9,812.5	9.8125	13.16	33,475	0.00981

Industry Applications of Power Units

⚡ Electrical Engineering

Watts and kilowatts are the standard. Circuit design requires precise power calculations for sizing wires, fuses, and transformers. Power factor (kW vs kVA) is critical for industrial installations. Three-phase motors are rated in kW globally and HP in the US market.

☀️ Solar & Renewable Energy

Solar panels are rated in watts peak (Wp) — the maximum output under standard test conditions. A residential system of 5 kWp produces approximately 20 kWh/day in India. Inverters are rated in kW or kVA. Battery storage is measured in kWh (energy), while charge/discharge rate is in kW (power).

🚗 Electric Vehicles

EV motors are rated in kW (continuous) and peak kW. A Tesla Model 3 has a 239 kW (320 HP) motor. Charging stations are rated in kW: Level 1 (1.4 kW), Level 2 (7–22 kW), DC Fast (50–350 kW). Battery capacity is in kWh, but charging speed is pure power (kW).

🏠 Household Appliances

Indian BEE star ratings are based on power consumption in watts. An inverter AC's EER (Energy Efficiency Ratio) is measured in BTU/hr per watt. Electricity bills charge per kWh (1 unit = 1 kWh). Running a 2 kW heater for 3 hours = 6 kWh = 6 units consumed.

🏭 Industrial Motors

Large motors are specified in HP (USA) or kW (international). A 50 HP motor = 37.3 kW. Motor efficiency matters: a 90% efficient 50 HP motor actually draws 41.4 kW from the supply. Variable Frequency Drives (VFDs) are rated by the motor kW/HP they can control.

❄️ HVAC Systems

Cooling capacity is measured in BTU/hour or tons of refrigeration (1 ton = 12,000 BTU/hr = 3.52 kW). However, the electrical power consumed by the compressor is always in watts/kW. COP (Coefficient of Performance) = cooling capacity (kW) ÷ power consumed (kW).

Power vs Energy: The Critical Difference

One of the most common confusions in electrical concepts is mixing up power and energy. They are related but fundamentally different:

Aspect	Power	Energy
Definition	Rate of energy transfer	Total amount of work done
SI Unit	Watt (W) = Joule/second	Joule (J) or kilowatt-hour (kWh)
Analogy	Speed of a car (km/hr)	Distance traveled (km)
Formula	P = E ÷ t	E = P × t
Electricity bill	Not directly billed	Billed per kWh (unit)
Example	100W bulb brightness	100W bulb ON for 10 hrs = 1 kWh

Common Mistake: "kWh" (kilowatt-hour) is NOT a unit of power — it's energy. Saying "this solar panel produces 5 kWh" is meaningless without a time frame. Correct: "5 kW panel produces ~20 kWh per day" or "5 kWp capacity."

Frequently Asked Questions

No, but they measure the same thing (power). One mechanical horsepower equals 745.7 watts. Horsepower was defined by James Watt in the 1700s to compare steam engine output to horses. Watts is the modern SI standard. Use HP for engines and motors in the US/UK, and kW for international specifications.

1 mechanical (UK) horsepower = 745.7 watts. 1 metric horsepower (PS) = 735.5 watts. 1 electrical horsepower = 746 watts exactly. The differences are small but matter in precise engineering calculations. For rough estimates, 1 HP ≈ 750 watts or ¾ of a kilowatt.

Historical convention. When steam engines replaced horses, James Watt marketed his engines in "horsepower" so buyers could easily compare to the horses they'd replace. The term stuck in automotive culture, especially in the US and UK. European manufacturers increasingly use kW alongside HP/PS. Electric vehicles often quote both kW and HP in specifications.

Solar panels use kilowatts peak (kWp) because it represents their maximum power output under standard test conditions (1000 W/m² irradiance, 25°C cell temperature). A 5 kWp system means it can produce up to 5,000 watts at peak sunlight. Actual output varies by time of day, weather, and panel orientation. Annual energy production (kWh) depends on location-specific sun hours.

Power is the rate of energy transfer (measured in watts), while energy is the total amount transferred over time (measured in joules or kWh). Think of it like water flow: power is the flow rate (liters/minute), energy is the total water collected (liters). A 100W device running for 10 hours uses 1 kWh of energy. Your electricity bill charges for energy (kWh), not power (kW).

No! kWh (kilowatt-hour) is a unit of energy, not power. It represents the energy consumed by a 1 kW device running for 1 hour. Power (kW) × Time (hours) = Energy (kWh). This is what your electricity meter measures and what appears on your bill as "units consumed." One unit = 1 kWh.

Formula: Energy (kWh) = Power (watts) ÷ 1000 × Hours used. Example: A 2000W heater running 3 hours/day for 30 days = (2000 ÷ 1000) × 3 × 30 = 180 kWh. At ₹8/unit, that's ₹1,440/month. This is why knowing device wattage is crucial for managing electricity costs.

1 ton of refrigeration = 12,000 BTU/hour of cooling capacity = 3,517 watts (≈3.5 kW) of cooling output. However, the AC doesn't consume 3.5 kW of electricity — a 5-star inverter 1-ton AC consumes only 700–900W due to its efficiency (EER/ISEER). The "ton" rating refers to cooling capacity, not electrical consumption.

Boiler horsepower (BHP) is a very different unit from mechanical HP. 1 boiler HP = 9,812.5 watts (about 13.2 mechanical HP). It was originally defined as the power needed to evaporate 34.5 pounds of water per hour at 212°F. Used exclusively in steam boiler specifications and industrial heating systems.

For 1 kW (1,000 watts) of solar capacity, you need approximately 2–3 panels (assuming 400–500W per modern panel). A 1 kW system produces about 4–5 kWh per day in India (4–5 units). For a typical home using 10 kWh/day, you'd need a 2–3 kWp system (5–7 panels). Space required: approximately 60–80 sq ft per kW.

HP (mechanical) = 745.7W, PS (metric) = 735.5W. The difference is about 1.4%. PS (Pferdestärke = "horse strength" in German) is used in European and Japanese car specifications. A car rated at 200 PS equals approximately 197 HP. When comparing specifications internationally, always check which standard is being used.

No. The inverter capacity must exceed the total load. A 1 kW (1000 VA) inverter can handle loads up to approximately 800W (accounting for power factor and efficiency losses). For a 2000W appliance, you need at least a 2.5 kVA inverter. Always add a 20–30% safety margin when sizing inverters: required inverter = total load × 1.25.