Power Converter
There are two horsepowers and they differ by 1.4%.
There are two horsepowers and they differ by 1.4%. Power across watts, horsepower, metric horsepower and BTU per hour.
Converted
100 horsepower (mechanical)
74,569.9872 watts · 74.57 kilowatts
There are two horsepowers. Mechanical horsepower is about 745.7 watts and metric horsepower (PS) about 735.5 — a 1.4% difference, which is why the same engine is quoted at slightly different figures in different markets. Watt chose the unit by measuring what a dray horse could actually lift.
How the Power Converter works
Power across watts, horsepower, metric horsepower and BTU per hour. Mechanical and metric horsepower differ by about 1.4%, which is why the same engine is quoted differently in different markets.
Also known as: horsepower to kw converter · kw to bhp converter · watts to horsepower · ps versus bhp difference
Two horsepowers, and where they came from
James Watt needed a comparison to sell steam engines against horses, so he measured what a dray horse could lift over time. Mechanical horsepower is about 745.7 watts, and it was a marketing unit from the start.
Metric horsepower (PS, from Pferdestärke) is defined slightly differently at about 735.5 watts. The 1.4% gap means the same engine carries different figures in different markets, which is why specifications quote both.
Brake horsepower is a third term, referring to how the measurement is taken rather than to the unit. It is measured at the crankshaft, so wheel horsepower is lower by the drivetrain losses.
Power against energy
Power is the rate of energy transfer; energy is power multiplied by time. A kilowatt is a rate and a kilowatt-hour is a quantity, which is why bills are in kilowatt-hours rather than kilowatts.
Confusing them is common and consequential. A 3 kW heater does not use 3 kW of electricity in a day. It uses 3 kW while running, and the daily energy depends entirely on how long it runs.
The same distinction separates a solar panel's watt-peak rating from its annual yield in kilowatt-hours. One is a maximum rate under test conditions; the other is the quantity actually delivered over a year.
Peak, continuous and power factor
Peak power is what equipment can produce briefly; continuous is what it can sustain without overheating. Marketing quotes peak, engineering uses continuous, and the gap can be a factor of two or more.
Power factor is an AC complication: the ratio of real power doing work to apparent power flowing. A poor power factor means current flows without useful effect, which is why industrial supplies are charged on it.
Voltage explains why kettles differ by country. A 230 V supply delivers more power through the same current limit than a 120 V one, so a 3 kW kettle is normal in Europe and impossible on a standard North American circuit.
Where to go next
The Power Converter question rarely arrives on its own. These are the ones that usually come with it:
- Energy Converter — A food calorie is a thousand physics calories.
- Torque Converter — A newton metre and a joule are not the same thing.
- Frequency Converter — 3,000 rpm and 50 Hz are the same frequency.
- Ring Size Calculator — Finger measurement to US, UK, EU and Japanese sizes.
Frequently asked questions
How many watts in a horsepower?
About 745.7 for mechanical horsepower and 735.5 for metric horsepower (PS). The 1.4% gap is why the same engine carries different figures in different markets.
Where does horsepower come from?
James Watt measured what a dray horse could lift over time, to give buyers a comparison for his steam engines. It was a marketing unit and it outlived the machines it was invented for.
What is the difference between power and energy?
Power is the rate of energy use; energy is power multiplied by time. A kilowatt is a rate, a kilowatt-hour is a quantity — which is why bills are in kilowatt-hours.
How do I convert BTU per hour to watts?
Multiply by 0.2931. A 12,000 BTU/h air conditioner is about 3.5 kW, which is the figure marketed as one ton of cooling.
Is PS the same as bhp?
No. PS is metric horsepower at 735.5 W; bhp is brake horsepower, which is the mechanical figure measured at the crankshaft. They are close and they are not the same number.
How much power does a person produce?
A fit cyclist sustains a few hundred watts and can peak far above that briefly. Sustained output over hours is well under a horsepower, which puts Watt's unit in perspective.
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