HP to CC Calculator
Work backwards from a horsepower target to the engine displacement that would realistically produce it — with the engine type doing the heavy lifting, because there's no universal hp-to-cc factor.
Planning an engine swap, speccing a kit car, or sizing a generator? Running the numbers backwards from a power target to a displacement is a useful sanity check — provided you accept from the outset that the same horsepower can come from wildly different engine sizes.
Why There Is No Single HP-to-CC Factor
Displacement only tells you how much air an engine can swallow per two crankshaft revolutions. How much power it makes from that air depends on how hard you can breathe through it, how fast you can spin it, and how much pressure you can put in it.
Specific output across engine types varies by nearly four times:
| Engine type | hp per liter | hp per cc | Why |
|---|---|---|---|
| Small utility engine | ~45 | 0.045 | Built for continuous duty at 3,600 rpm, cheap to make, long service life |
| Economy car, NA | ~60 | 0.060 | Tuned for fuel economy and low-rpm drivability |
| Modern NA car | ~80 | 0.080 | Variable valve timing, direct injection, higher compression |
| Performance NA | ~110 | 0.110 | High revs, aggressive cams, individual throttle bodies |
| Turbocharged car | ~130 | 0.130 | Forced induction adds air mass beyond swept volume |
| Sport motorcycle | ~170 | 0.170 | 14,000+ rpm redline, short stroke, minimal durability margin |
Pick the wrong row and your estimate is out by a factor of three. That's the whole reason this page has a dropdown instead of a single multiplier.
Reverse: HP = cc × (HP per cc) — see the CC to HP calculator
HP to CC Chart by Engine Type
Displacement in cc needed for each power target, by engine category.
| Target HP | Utility | Economy NA | Modern NA | Performance NA | Turbo | Sport bike |
|---|---|---|---|---|---|---|
| 25 | 560 | 420 | 310 | 230 | 190 | 150 |
| 50 | 1,110 | 830 | 630 | 450 | 380 | 290 |
| 75 | 1,670 | 1,250 | 940 | 680 | 580 | 440 |
| 100 | 2,220 | 1,670 | 1,250 | 910 | 770 | 590 |
| 150 | 3,330 | 2,500 | 1,880 | 1,360 | 1,150 | 880 |
| 200 | 4,440 | 3,330 | 2,500 | 1,820 | 1,540 | 1,180 |
| 250 | 5,560 | 4,170 | 3,130 | 2,270 | 1,920 | 1,470 |
| 300 | 6,670 | 5,000 | 3,750 | 2,730 | 2,310 | 1,760 |
| 400 | 8,890 | 6,670 | 5,000 | 3,640 | 3,080 | 2,350 |
| 500 | 11,110 | 8,330 | 6,250 | 4,550 | 3,850 | 2,940 |
| 700 | 15,560 | 11,670 | 8,750 | 6,360 | 5,380 | 4,120 |
What Boost Actually Changes
A turbocharger doesn't make the cylinders bigger. It packs more air mass into the same swept volume, so the engine behaves as if it were larger — which is why the turbo column sits so far left of the naturally aspirated ones.
Roughly, at moderate pressure ratios, a boosted engine behaves like a naturally aspirated one of displacement scaled by the absolute pressure ratio:
- 0.5 bar (7 psi) — behaves like about 1.5× the displacement
- 1.0 bar (14.7 psi) — roughly 2× the displacement
- 1.5 bar (22 psi) — roughly 2.5×, though charge cooling and knock limits start to bite hard
Real engines fall short of these ideals because of intercooler efficiency, exhaust backpressure and the need to run richer and retard timing under boost. For a proper estimate use the boost horsepower calculator or NA to boosted.
A Better Yardstick Than HP per Liter
Specific output is the metric everyone quotes and it quietly rewards the wrong thing. Power is torque × speed, so an engine that revs to 14,000 rpm posts a spectacular hp-per-liter figure while making modest torque — which is exactly why sport motorcycle engines top the table above.
Brake mean effective pressure normalises for engine speed and describes how hard each cylinder actually works per cycle. Typical BMEP values:
- Naturally aspirated road engines: roughly 10–13 bar
- Well-developed NA performance engines: 13–15 bar
- Modern turbocharged road engines: 20–25 bar
By BMEP, a 170 hp/liter sport bike engine and a 130 hp/liter turbo car engine aren't remotely comparable — the turbo is working its cylinders far harder, it just does so at 6,000 rpm rather than 14,000. Our hp per liter calculator and volumetric efficiency tools go further into this.
Where This Estimate Is Genuinely Useful
- Engine swaps — checking whether a target output is plausible from a candidate engine before you buy it
- Kit cars and specials — sizing a donor engine to a power goal and a weight budget
- Generators and pumps — the utility row is realistic for continuous-duty industrial engines
- Sanity-checking a claim — a 1,600 cc naturally aspirated engine claiming 250 hp implies 156 hp/liter, which is race-engine territory and should invite questions
Where it isn't useful: predicting a specific engine's output. For that, measure it or read the manufacturer's figure. This is a feasibility check, not a dyno.
Related Calculators
For the forward direction see CC to HP. To calculate displacement from bore and stroke use the engine displacement calculator, and to move between cc, liters and cubic inches try the engine size converter.
Frequently Asked Questions
Divide horsepower by the specific output for that engine type. A modern NA car makes ~0.08 hp/cc, so 200 hp ≈ 2,500 cc.
From about 590 cc (sport bike) to 2,220 cc (utility engine). Modern NA car ≈ 1,250 cc; turbo ≈ 770 cc.
No. Specific output ranges from ~45 to over 170 hp per liter depending on technology. Any single factor is only valid inside one category.
About 6,250 cc naturally aspirated or 3,850 cc turbocharged at typical modern outputs.
Substantially — forced induction typically lifts output from ~80 to ~130 hp/liter, which is why a 2.0 turbo matches a 3.0 NA.
It rewards revs, not efficiency. A 14,000 rpm engine posts a huge figure on modest torque. BMEP normalises for speed and compares fairly.
cc ÷ 1,000 = liters; cc ÷ 16.387064 = cubic inches. So 5,700 cc = 5.7 L ≈ 348 ci.
Yes — use the utility setting (~45 hp/L). Continuous-duty industrial engines run modest speeds and deliberately low specific output.