What is power?

Power is the rate of energy transfer – how much energy per unit time. While energy is ‘how much work was done’, power is ‘how fast work is being done’. 1 watt = 1 joule per second. A 60-watt light bulb uses 60 joules of energy every second. A 100-watt heater warms faster than a 50-watt one. Power is measured in watts (W) for electrical and most modern uses, kilowatts (kW) for appliances and engines, megawatts (MW) for industrial scale, horsepower for engines (especially in US), BTU per hour for HVAC systems. Understanding power helps with: sizing electrical appliances, comparing engine performance, calculating energy bills, designing solar systems, and choosing the right air conditioner for room size.

How to use this tool

1. Enter value — Power amount to convert.
2. Select ‘from’ unit — Watts (W), kW, MW, mechanical hp, metric hp (PS), BTU/h, ft-lb/s, cal/s.
3. Read conversions — All other units update instantly with equivalents.

Power unit conversions

All conversions via watt (SI base):

• 1 W = 1 J/s
• 1 kW = 1,000 W
• 1 MW = 1,000 kW = 1,000,000 W
• 1 mechanical hp = 745.7 W (US engine convention)
• 1 metric hp (PS) = 735.5 W (European cars, ‘Pferdestarke’)
• 1 BTU/h = 0.293 W (HVAC convention)
• 1 ft-lb/s = 1.356 W (mechanical engineering)

Useful reference:

• 1 kW ≈ 1.34 hp ≈ 3,412 BTU/h
• 1 hp ≈ 750 W ≈ 0.75 kW (memorize)
• 1 ton AC = 12,000 BTU/h = 3.516 kW (refrigeration unit)

Examples

Common power ratings:

• LED bulb: 7-15 W
• Mobile phone charger: 5-65 W (USB-C fast charging)
• Laptop: 30-100 W (varies by load)
• Refrigerator: 100-400 W
• 1 hp motor: 745.7 W ≈ 0.75 kW
• Air conditioner (1 ton): 3,516 W ≈ 3.5 kW
• Hair dryer: 1,200-2,000 W
• Microwave: 600-1,200 W
• Electric kettle: 1,500-3,000 W
• Car engine: 50-300 hp = 37-224 kW
• F1 car: 1,000+ hp = 750+ kW
• Wind turbine (utility): 2-5 MW
• Coal power plant: 500-1,500 MW

Tips & best practices

• Inverter AC ratings in ‘tons’ = cooling power. 1 ton = 12,000 BTU/h = 3.5 kW. Match ton to room size: 1 ton for 100-150 sq ft, 1.5 ton for 150-250 sq ft, 2 ton for 250-400 sq ft
• Generator/inverter sizing: total VA (volt-amperes) must exceed sum of all running appliances. Add 30% headroom
• Solar panel output rated in watts (peak). 300W panel produces 300W under ideal sunlight – usually 4-5 hours/day equivalent
• EV charging speed: Level 1 (1.4 kW), Level 2 (7-22 kW), DC fast charging (50-350 kW). Time to charge = battery kWh / charge rate
• Engine ‘hp vs torque’: hp measures rate of work, torque is rotational force. Both matter but for different things (top speed vs acceleration)
• Higher peak power doesn’t mean higher energy use – depends on duration. A 2000W heater used 1 hour uses same energy as 1000W heater used 2 hours (2 kWh)
• When buying appliances, check ‘rated power’ (typical use) vs ‘peak power’ (instantaneous max) – rated matters for energy bills

Limitations & notes

Many appliances have varying power consumption – the rated power is the peak, average use is lower. Inverter ACs vary from 30% to 100% of rated power based on cooling demand. Power factor (relevant for AC electricity, especially industrial) affects effective vs apparent power – this calculator handles real (active) power only.

Frequently Asked Questions

What’s the difference between watts and watt-hours?

Watts (W) is power – rate of energy use. Watt-hours (Wh) is energy – total energy used. A 100W bulb running for 5 hours uses 500 Wh = 0.5 kWh of energy. Electricity bills are in kWh (energy), but bulbs are rated in W (power).

How is ‘horsepower’ different from kW?

Both measure power. 1 hp ≈ 0.7457 kW (mechanical hp, US/UK). 1 metric hp (PS) ≈ 0.7355 kW (European cars). The slight difference is historical – mechanical hp was defined as the work an average horse could do; metric hp was a slightly different definition. For practical purposes, treat them as equivalent.

Why is AC capacity measured in tons?

Historical convention from ice-cooling days. 1 ton refrigeration = the cooling power needed to freeze 1 short ton (2,000 lb) of water in 24 hours = 12,000 BTU/h = 3.516 kW. Modern AC labels show both ton rating and BTU/h or kW for clarity.

What size generator do I need for my home?

Add up max simultaneous loads. Typical home: 1-2 lights (40W), 1-2 fans (50W each), TV (100W), refrigerator (300W intermittent), maybe AC (1500W). For full home use: 3-5 kVA inverter generator. For just essentials during power cuts: 1-2 kVA UPS or generator.

Is higher wattage always better for appliances?

Not necessarily. Higher wattage means more electricity used = higher bill. Match power to need: laptop 60W vs gaming PC 600W both work but for different needs. For lighting, fewer watts (LED) gives same brightness with much less energy.

How do I calculate solar panel needs?

Daily energy need (kWh) / daily peak sun hours (4-5 in India) / panel efficiency (~85%) = total panel wattage needed. Example: 10 kWh/day / 4.5 / 0.85 = 2,610W panels needed. Round up to 12 panels of 250W = 3 kW system.

Why do gym treadmills list horsepower?

Marketing – the motor’s peak power. ‘Continuous duty’ rating (the real number that matters) is usually lower. A 2.5 hp continuous duty motor handles a 100 kg runner just fine. ‘Peak hp’ or ‘starting hp’ figures are marketing exaggerations – look for CHP or continuous hp.

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