BHP to HP Converter
Brake horsepower and horsepower are the same unit — the conversion factor is 1. What changes is where the reading was taken, so this tool shows the same figure as hp, PS, kW and wheel horsepower together.
"BHP to HP" is one of those searches where the honest answer is shorter than the question. There's nothing to convert — the two labels describe the same unit. But people keep searching it because spec sheets, adverts and dyno printouts disagree with each other, and the letters look like they should explain why. They do, just not the way most people expect.
Why 1 bhp Equals 1 hp
James Watt defined horsepower in the 1780s as 33,000 foot-pounds of work per minute — 550 foot-pounds per second — while selling steam engines to mill owners who thought in horses. That definition never changed. Convert it to SI and you get 745.699872 watts, and that's the value behind both labels.
"Brake" horsepower borrowed its name from the Prony brake, an 1821 friction dynamometer that clamped a band around a flywheel and measured how hard you had to hold it back. The measurement told you the engine's torque; multiply by speed and you've power. Water brakes and eddy-current absorbers replaced the friction shoe long ago, but the name survived.
What Actually Differs Between the Numbers You See
If two figures for one car disagree, one of four things is going on — and none of them is the bhp-versus-hp distinction.
| Cause of the gap | Typical size | How to spot it |
|---|---|---|
| One figure is PS, not bhp | PS reads ~1.4% higher | Round continental numbers: 150, 200, 245, 310, 510 |
| One figure is wheel power | 11–23% lower | Comes from a rolling road, quoted as whp, rwhp or rwkw |
| One figure is SAE gross | 15–25% higher | US car, model year 1971 or earlier |
| Different correction factor | 1–4% | SAE J1349 vs DIN vs uncorrected dyno output |
Crankshaft, wheels, and the gap between them
Every gear mesh, bearing, universal joint and tire sidewall between the flywheel and the roller takes a cut. Brake horsepower is measured before any of that; wheel horsepower after all of it. The usual working numbers are 11% for front-wheel drive, 15% for rear-wheel drive and around 23% for all-wheel drive, though a torque-converter automatic under light load can lose a lot more.
That gap is why a car honestly rated at 300 bhp will show roughly 255 whp on a rear-wheel-drive rolling road and nobody has been misled. Our drivetrain loss calculator works the percentage out from a measured pair, and wheel HP vs crank HP covers why the loss isn't a fixed percentage in reality.
Gross vs Net: The Reason Old Muscle-Car Figures Look Absurd
Until the 1972 model year, American manufacturers quoted SAE gross horsepower. The test engine ran on a stand with no alternator charging, no production exhaust, no cooling fan and often optimized timing. Everything that normally steals power was simply absent.
From 1972 the industry moved to SAE net, measured with the full production accessory set installed. Published figures dropped 15–25% overnight on unchanged engines. Modern SAE J1349 certified ratings go further still, requiring witnessed testing and a standard correction to 29.23 inHg dry pressure and 77 °F.
Europe's equivalent is ECE R85 (implementing EC Directive 80/1269), which is also a net standard and lands close enough to SAE net that the two are broadly comparable. Comparing either against a 1969 gross rating isn't a fair fight. See how horsepower is measured and the SAE correction factor calculator for the detail.
A Footnote: RAC Horsepower, the Reason Britain Says "bhp"
Between 1910 and 1947 British cars were taxed on RAC horsepower, a formula based only on cylinder bore and count — it ignored stroke, compression and rpm entirely. A "12 hp" Austin was a tax classification, not a performance claim, and the two numbers could differ by a factor of three.
British makers started writing "brake horsepower" specifically to signal this is the real, measured figure, not the tax one. The tax formula died in 1947; the habit of writing bhp never did. It also explains why French and Belgian paperwork still uses chevaux fiscaux — the same idea, still alive.
Converting to Units That Genuinely Differ
Since bhp and hp need no conversion, the useful moves are sideways: bhp to kW for registration paperwork, bhp to PS for continental spec sheets, and whp to hp to bring a rolling-road figure back to the crankshaft. The horsepower unit converter shows all of them at once.
Frequently Asked Questions
Yes. Both are 745.699872 W, so the factor is 1.0. A 300 bhp engine and a 300 hp engine make the same power.
Context, not size. bhp declares the reading came from the crankshaft on a brake dyno. Plain hp says nothing about where it was taken, so it can mean crank power, wheel power or marketing.
History. Britain taxed cars on the RAC horsepower formula until 1947, so makers wrote "brake horsepower" to mean the measured figure. In the US, SAE J1349 net became the label and plain "hp" stuck.
Always. Roughly 11% higher on FWD, 15% on RWD and 23% on AWD, because whp is read after the whole drivetrain.
Numerically identical. The only way they would differ for one car is if one figure was really PS (1.4% smaller unit) or a wheel reading.
Pre-1972 SAE gross ratings ran the engine with no alternator, exhaust or fan — about 15–25% optimistic versus modern net figures. That's why muscle-car numbers look inflated today.
Under modern net standards — SAE J1349 and ECE R85 — yes. The engine runs with production accessories driven, so their draw is already subtracted.