There is no single number that converts CC to HP. An engine’s horsepower depends on far more than its size: aspiration (naturally aspirated vs. turbo or supercharged), state of tune, compression, fuel, and the RPM where it makes peak power. The most reliable way to estimate it is to use the engine’s specific output – its horsepower per litre – in this formula: HP = (CC ÷ 1000) × HP per litre. A modern naturally-aspirated car makes roughly 80 HP per litre (the default this calculator uses), but real engines run from about 30 HP/L for lawn-mower and utility engines, up to 150+ HP/L for turbo and sportbike engines and 300+ HP/L for race engines. Enter your displacement in CC (or litres), pick the HP-per-litre figure for your engine type from the table below, and the calculator returns horsepower and kW; leave it at 80 HP/L for a modern naturally-aspirated estimate.
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How to convert CC to HP (the real formula)
The honest conversion uses the engine’s specific output (horsepower per litre):
HP = (CC ÷ 1000) × HP per litre
and to work backwards from a power target:
CC = (HP ÷ HP per litre) × 1000
The only judgement call is the HP-per-litre figure. That one number captures everything displacement cannot: a 1.0-litre lawn-mower engine and a 1.0-litre superbike engine have the same CC but make 4 to 5 times different power because their specific output is so different. This is why the popular “divide by 15” shortcut (which is the same as assuming about 67 HP per litre) is fine for older, low-stress engines but badly under-reads a modern turbo or motorcycle engine.
CC to HP by engine type
Pick a realistic HP-per-litre figure for the calculator from the engine class that matches yours. The “CC per HP” column is the same relationship expressed the other way (CC per HP = 1000 ÷ HP-per-litre), which is where rules of thumb like “15 CC per HP” come from.
| Engine type | Typical specific output | ≈ CC per HP | Example |
|---|---|---|---|
| Lawn mower, generator, small utility | 20–40 HP/L | 25–50 | 160 CC ≈ 4–5 HP |
| Outboard & older low-stress car/truck V8 | 40–60 HP/L | 17–25 | 5.0 L V8 ≈ 250 HP |
| Modern naturally-aspirated car | 60–90 HP/L | 11–17 | 2.0 L ≈ 160 HP |
| Turbocharged car | 95–130 HP/L | 8–11 | 2.0 L turbo ≈ 250 HP |
| Naturally-aspirated sportbike | 110–160 HP/L | 6–9 | 600 CC ≈ 95 HP |
| Superbike / high-performance | 150–200 HP/L | 5–7 | 1,000 CC ≈ 200 HP |
| Race / heavily boosted | 200–300+ HP/L | 3–5 | Purpose-built |
CC to HP conversion examples
CC to HP
- 1,000 CC, modern NA car (80 HP/L): (1000 ÷ 1000) × 80 = 80 HP.
- The same 1,000 CC as a superbike (150 HP/L): 1.0 × 150 = 150 HP – identical displacement, nearly double the power.
- 4,500 CC V8 at the default 80 HP/L: 4.5 × 80 = 360 HP (a low-stress truck tune nearer 55 HP/L gives about 248 HP).
- 2,000 CC turbo (120 HP/L): 2.0 × 120 = 240 HP.
Horsepower to CC (reverse conversion)
Working backwards from a power target uses CC = (HP ÷ HP per litre) × 1000:
- ~150 HP from a naturally-aspirated engine (~85 HP/L): (150 ÷ 85) × 1000 ≈ 1,765 CC (about 1.8 L).
- ~150 HP from a turbo engine (~120 HP/L): (150 ÷ 120) × 1000 ≈ 1,250 CC (about 1.25 L) – forced induction reaches the same power with less displacement.
FAQs
Q: How do you convert CC to HP?
A: Use the engine’s specific output: HP = (CC ÷ 1000) × HP per litre. Pick the HP-per-litre figure from the engine-type table (about 80 HP/L for a modern naturally-aspirated car). There is no single fixed multiplier because horsepower depends on the engine’s design, not just its size.
Q: What is the “CC divided by 15” rule, and is it accurate?
A: Dividing CC by 15 assumes roughly 67 HP per litre. It is a reasonable rough guess for older, low-stress engines, but it under-reads a modern naturally-aspirated engine (~80 HP/L) and significantly under-reads turbocharged or sportbike engines. Use a specific-output figure that matches your engine for a realistic estimate.
Q: How do I convert horsepower to CC (the reverse)?
A: Rearrange the formula: CC = (HP ÷ HP per litre) × 1000. For example, 150 HP from a naturally-aspirated engine at 85 HP/L needs about (150 ÷ 85) × 1000 ≈ 1,765 CC (around 1.8 litres).
Q: Can I use litres or cubic inches instead of CC?
A: Yes. The calculator has a litres option in the unit selector. For cubic inches, convert first: 1 cubic inch = 16.387 CC (for example, a 350 ci V8 is about 5,735 CC).
Q: How accurate is a CC to HP estimate?
A: Treat it as a planning estimate, not a measured figure. Actual dyno horsepower depends on aspiration, tuning, compression, fuel, the RPM where peak power is made, altitude, and engine condition. Matching the specific output to your engine type gets you in the right range.
CC vs HP: what each number tells you
CC tells you how big an engine is; horsepower tells you what it does with that size. Bridge the two with specific output (HP per litre): start from the engine-type table, multiply by the displacement in litres, and you have a realistic estimate in either direction. The single fixed “divide by 15” answer is only ever a rough starting point – the specific-output approach is what makes the number trustworthy.