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Engine Compression Ratio Calculator

Static compression ratio from bore, stroke and chamber volume, with gasket and piston corrections.

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Engine Compression Ratio Calculator works straight from this page — free, instant, nothing to install. It sits under Running costs in our catalogue, alongside Headlight Beam Distance Calculator and RV Loan Calculator.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What is Engine Compression Ratio Calculator?

Static compression ratio from bore, stroke and chamber volume, with gasket and piston corrections.

When would I actually use this?

Deciding between two cars, or between keeping one and replacing it: fuel or charging, insurance, depreciation and what a kilometre really costs.

What is the most common mistake?

Comparing on fuel alone. Depreciation is usually the largest line in the first years and dwarfs the difference in consumption between two comparable cars.

Is there a tool for the next step?

RV Loan Calculator is the closest one after this: Payment, total cost and depreciation outlook for a motorhome, campervan, travel trailer, fifth wheel or pop-up, over terms up to twenty years. Trade-in and sales tax are handled separately from the down payment, and the tool marks the year the loan balance finally falls below the vehicle's likely value.

What else is worth having open alongside it?

Stopping Distance Calculator and Trailer Tongue Weight Calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

The arithmetic is exact for the prices and consumption you enter. Manufacturer figures are measured on a standard cycle and real-world consumption is routinely 10% to 25% higher.

Further reading

All guides →
ExplainerCompression Ratio, and What Actually Limits ItEfficiency rises with compression ratio, so why do petrol engines stop around 12:1? Because compressing a charge heats it — r to the power of gamma minus one — and above a certain temperature the unburnt end gas lights itself.ExplainerFiscal Horsepower Is Not HorsepowerSeveral European countries tax cars on an administrative power figure that nobody has ever measured — it is the output of a formula, the formula differs by country, and it has been rewritten more than once. Here is what each market actually taxes, worked through on one car.ExplainerEngine Displacement and Compression Ratio: What They Actually Tell YouBoth numbers are pure geometry — one is the volume a piston sweeps, the other a ratio of two volumes — and both are read as if they described power. Here is each derivation worked on real engines, and exactly what each number can and cannot support.ComparisonLeasing, Hire Purchase or Cash: the Five-Year Total, Not the Monthly PaymentThree ways to put the same car on the drive, priced over five years at the same interest rate. The monthly payments rank the options in exactly the reverse order of what they cost — and the gap turns out to be a single, computable number.ExplainerA Company Car Is Pay: What the Benefit in Kind Costs You in France, Germany and ItalyNobody negotiates a company car as a pay cut, but that is what the tax treatment makes it. Three countries value the same car by three completely different methods, one of them changed in 2025 in a way that nearly doubled the figure, and in all three an electric car is taxed at a fraction of the same vehicle with an engine.ExplainerHeadlight Aim and How Far You Can Actually SeeA dipped beam is aimed downward by a fraction of a degree, so its reach on flat road is a single division. Do it and you find that at motorway speed the beam is shorter than the stopping distance — and that a loaded boot can throw the whole calculation away.