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Power-to-Weight Ratio Calculator

HP/ton, kW/kg — and a 0-100 km/h estimate.

Power-to-weight ratio (P/W) is the single number that predicts how fast a car accelerates better than peak horsepower, torque, or any other metric. A lightweight car with modest power beats a heavy car with big power almost every time — the numbers don't lie.

Power-to-weight
200.0 hp/ton(0.149 kW/kg)
hp/lb
0.0907
Power (hp)
300.0
Weight (kg)
1500
Rough 0-100 km/h
~7.3 s

Spirited family car. Capable without being scary.

Why P/W Beats Raw Horsepower

Horsepower moves the car. Weight resists that motion. The ratio of the two — hp per ton or kW per kg — is the true acceleration metric. This is why a 1,200 kg Lotus Elise with 220 hp feels faster than a 1,900 kg saloon with 300 hp, even though the saloon has 36% more power.

  • Lotus Elise 220: 220 hp / 1.2 ton = 183 hp/ton → 0-100 in ~5.5s
  • BMW 5-series 330i: 258 hp / 1.65 ton = 156 hp/ton → 0-100 in ~6.0s
  • A 100 kg weight reduction has the same effect as adding ~17 hp at 170 hp/ton
  • Every 10% weight reduction = same P/W gain as 10% more power

P/W Benchmarks for Real Cars

These reference points help you interpret where your car (or project car) sits in the performance hierarchy.

  • 100–150 hp/ton: economy hatchbacks, base-spec family cars
  • 150–250 hp/ton: performance saloons, GTIs, sport compacts
  • 250–350 hp/ton: fast cars — 0–100 in the 4–6s range
  • 350–500 hp/ton: supercars — Porsche 911 Turbo S (~480), Ferrari 488 (~405)
  • 500+ hp/ton: hypercars — Bugatti Veyron (530), Koenigsegg Agera RS (900+)
  • Formula 1: approximately 1,400 hp/ton — in another universe entirely

How to Improve Your P/W Ratio

Two levers: add power or lose weight. Weight reduction is almost always cheaper per hp/ton gained — and it improves handling, braking, and fuel economy as a bonus.

  • Lightweight wheels: 1 kg off rotating mass = ~5 kg equivalent off static weight
  • Remove spare tire + replace with foam kit: saves 10–15 kg
  • Carbon fibre hood, doors, or roof: 5–20 kg saving each
  • Engine tune/remap: 10–15% power increase for £300–500 on most turbocharged cars
  • Turbo upgrade: 30–60% power increase, but requires supporting mods (fuel, injectors, intercooler)

The Limits of the P/W Formula

P/W ratio predicts straight-line acceleration reasonably well but ignores everything that makes a car fast in the real world: traction, aerodynamics, drivetrain efficiency, and driver skill.

  • AWD vs RWD: AWD cars launch harder below 80 km/h, often beating their P/W prediction
  • Torque shape matters: a diesel's low-RPM torque vs a screaming VTEC Honda at the same P/W feel completely different
  • Aero: above 150 km/h, drag is the dominant limiter — P/W becomes less relevant at top speed
  • Traction limit: on wet roads or bad tyres, a high-P/W car may be slower than a lower-P/W AWD car

How to Calculate Power-to-Weight Ratio

Three steps to calculate your car's power-to-weight ratio and 0-100 estimate.

  1. 1
    Find your car's power output
    Use the manufacturer's spec sheet. US specs quote hp (SAE); European specs usually quote PS or kW. Select the correct unit in the calculator above.
  2. 2
    Find kerb weight and add driver
    Kerb weight is on the spec sheet or door sticker. Add 75–80 kg for a single driver. Race/track weights sometimes add a full tank of fuel (~50 kg).
  3. 3
    Interpret the result
    Compare your hp/ton figure to the benchmarks above. The rough 0-100 estimate assumes a RWD or AWD car on dry tarmac with a competent launch — add 0.5–1s for FWD cars and deduct 0.3–0.5s for launch-control AWD.
  4. 4
    Model modifications
    Use the calculator to model the effect of a tune, turbo upgrade, or weight reduction before spending money. See exactly how many hp/ton each modification buys you.

FAQ

Why is power-to-weight more useful than just horsepower?
Because the same engine in a lighter car accelerates harder. A 300 hp Miata would dust a 300 hp truck. P/W is what actually predicts performance.
Should I include driver weight?
Yes — add 75-80 kg for the driver. Manufacturer specs quote kerb weight (empty), but real-world acceleration happens with a body in the seat.
How accurate is the 0-100 estimate?
Rough — within a second or two for typical RWD/AWD cars. Launch technique, traction, and transmission type (DCT vs manual vs auto) can easily shift the real number.
What P/W ratio is considered fast?
250+ hp/ton is spirited; 350+ hp/ton is genuinely quick (sub-5 second 0-100); 500+ hp/ton is supercar territory. A Porsche 911 Turbo S is around 480 hp/ton; a Bugatti Veyron clears 530.
What is PS vs hp?
PS (Pferdestärke) is metric horsepower, used in Germany and other European countries. 1 PS = 0.9863 hp — almost identical. German car specs quote PS; US specs quote hp (SAE). The difference is less than 2% and rarely matters in practice.

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