Horsepower Calculator & Power to Weight Ratio
A complete horsepower calculator that solves for power to weight ratio, converts between hp, kW, and watts, calculates thrust to horsepower, and covers every power unit conversion — with step-by-step working for every result.
Enter power and weight to get the ratio in W/kg, hp/lb, and kW/tonne simultaneously. Formula: PWR = Power ÷ Weight
Power to Weight Ratio Report
Generated:
What is Horsepower?
Horsepower (hp) is a unit of power that measures the rate at which work is done. It was coined by Scottish engineer James Watt in the late 18th century to help market his steam engines to coal mine operators who were used to thinking in terms of how many horses their machinery could replace. Watt observed that a mine horse could turn a mill wheel 144 times per hour, working at a rate he calculated to be approximately 33,000 foot-pounds of work per minute.
Types of Horsepower
- Mechanical horsepower (hp): The original definition. 1 hp = 745.7 W. Used in the United States for engines, pumps, and electric motors.
- Metric horsepower (PS or CV): Defined as 75 kgf·m/s = 735.499 W. Used in Europe on vehicle datasheets. Slightly less than mechanical hp.
- Brake horsepower (BHP): The actual power delivered at the crankshaft, measured using a dynamometer (brake). Slightly less than indicated horsepower due to mechanical friction. BHP is the most commonly quoted figure for car engines in the UK.
- Indicated horsepower (IHP): Theoretical power based on cylinder pressure — always higher than BHP.
- Wheel horsepower (WHP): Power measured at the wheels — always lower than BHP due to drivetrain losses (typically 10–20%).
80 hp in kW? Simply multiply by 0.7457: 80 × 0.7457 = 59.66 kW. Conversely, 1 kW = 1.341 hp. So a 100 kW electric motor produces 134.1 hp.
Power to Weight Ratio Explained
The power to weight ratio (PWR) is one of the most important performance metrics in mechanical engineering, motorsport, aviation, and cycling. It measures how much power a machine or vehicle generates per unit of its own mass. A higher power to weight ratio means better acceleration, climbing ability, and overall performance.
Real-world examples illustrate why this matters so powerfully:
- Sports car (300 hp, 1,400 kg): P = 300 × 745.7 = 223,710 W | PWR = 223,710 ÷ 1,400 = 159.8 W/kg
- Bicycle + rider (0.4 kW, 80 kg): PWR = 400 ÷ 80 = 5 W/kg (elite level)
- Formula 1 car (~1,000 hp, 798 kg inc. driver): PWR = 745,700 ÷ 798 ≈ 934 W/kg
- GE90 jet engine (~93,000 lb thrust at cruise): At 500 knots ≈ 257 m/s → Power ≈ 10.5 MW per engine
In cycling, a PWR above 6 W/kg is elite Tour de France level. In cars, anything above 200 W/kg (≈150 hp/tonne) is considered sporty. Fighter jets achieve over 1,000 W/kg.
Worked Examples
How to Calculate HP from Torque & RPM
Formula: HP = (Torque × RPM) ÷ 5252
The constant 5252 comes from unit conversion: 33,000 ft·lbf/min ÷ (2π) ≈ 5252.
Example: Engine produces 350 ft·lbf at 5,500 RPM.
How to Convert HP to Kilowatts
Formula: kW = HP × 0.7457
One mechanical horsepower equals exactly 745.7 watts = 0.7457 kW.
Example: A 200 hp engine.
Power to Weight Ratio of a Car
Formula: PWR = Power (W) ÷ Mass (kg)
First convert hp to watts: multiply by 745.7. Then divide by mass.
Example: 450 hp sports car, 1,350 kg.
P = 450 × 745.7 = 335,565 W
Convert Thrust (Newtons) to HP
Formula: Power (W) = Thrust (N) × Velocity (m/s)
Then convert watts to hp: divide by 745.7.
Example: 22,000 N thrust at 200 m/s.
P = 22,000 × 200 = 4,400,000 W = 4,400 kW
What Does 80 HP Mean in kW?
Multiply horsepower by 0.7457 to get kilowatts.
kW = HP × 0.7457
Example: 80 hp engine (typical small hatchback).
How to Convert CC to BHP
There is no exact formula — it depends on engine type, tuning, and technology. A general rule of thumb is 1 BHP per 15–17 cc of displacement for naturally aspirated engines.
Example: 2,000 cc (2.0L) engine at 16 cc/BHP.
What is kW/ton and How to Convert to COP?
kW/ton is the efficiency of air conditioning or refrigeration equipment. Lower is better. COP (Coefficient of Performance) is the inverse measure — higher is better.
COP = 3.517 ÷ kW/ton
Example: AC unit rated at 1.2 kW/ton.
HP from Force & Speed
Formula: HP = (Force lbf × Speed ft/s) ÷ 550
The constant 550 comes from the definition: 1 hp = 550 ft·lbf/s.
Example: 800 lbf force at 40 ft/s.
Horsepower Comparison Table
To put horsepower figures in context, here is a reference table of typical power outputs across a wide range of machines:
| Machine / Source | Typical HP | Kilowatts (kW) | W/kg (est.) |
|---|---|---|---|
| Human — casual cycling | 0.1 hp | 0.075 kW | ~1 W/kg |
| Human — elite cyclist (sprint) | 0.5 – 2.0 hp | 0.37 – 1.5 kW | 15–20 W/kg |
| Small motorcycle (125cc) | 10 – 30 hp | 7.5 – 22 kW | 50–100 W/kg |
| Motorcycle (600–1000cc) | 80 – 200 hp | 60 – 149 kW | 300–600 W/kg |
| Family car (1.5–2.0L) | 100 – 200 hp | 75 – 149 kW | 50–100 W/kg |
| Sports car (e.g. Porsche 911) | 300 – 600 hp | 224 – 447 kW | 150–300 W/kg |
| Supercar (e.g. Bugatti Chiron) | 1,000 – 1,500 hp | 746 – 1,119 kW | 500–700 W/kg |
| Formula 1 car (2024 PU) | ~1,000 hp | ~746 kW | ~900 W/kg |
| Large diesel locomotive | 3,000 – 6,000 hp | 2,237 – 4,474 kW | 10–30 W/kg |
| Commercial jet engine (single) | ~10,000 – 75,000 hp | 7,500 – 55,928 kW | ~3,000 W/kg |
| Large container ship engine | ~100,000 hp | ~74,570 kW | ~5 W/kg |
| Saturn V rocket (first stage) | ~160,000,000 hp | ~120,000,000 kW | Very high |