RWKW to HP Calculator
Australian and New Zealand dyno sheets report power in rear-wheel kilowatts. This converts rwkw into wheel horsepower and an estimated flywheel figure in both kW and bhp.
If you've spent any time on an Australian car forum you've seen numbers like "made 280rwkw on 98" quoted with no further explanation. The unit is real, the notation is standard, and it isn't the same thing as the kilowatt figure on a spec sheet — which is exactly why the conversion trips people up.
What RWKW Actually Is
RWKW = rear-wheel kilowatts. It is a chassis dynamometer reading taken at the tire contact patch, expressed in kilowatts because Australia and New Zealand went metric for engine power and never adopted horsepower on paperwork.
The critical distinction: a manufacturer's kW figure is crankshaft power measured on an engine dyno to ECE R85. RWKW is what survives after the gearbox, tailshaft, differential, wheel bearings and tire deformation have each taken a cut. For the same car, rwkw is always the smaller number — usually 15% smaller on a rear-drive manual.
So "a 250 kW Commodore made 205rwkw" isn't a broken car. It is a completely normal car, described in two different units at two different points in the driveline.
Divide to remove the loss — multiplying by (1 + loss) understates the engine
RWKW Conversion Chart
Wheel horsepower is a straight unit conversion and is exact. The flywheel columns assume a 15% rear-wheel-drive drivetrain loss and are estimates.
| RWKW | RWHP (exact) | Flywheel kW (est.) | Flywheel bhp (est.) |
|---|---|---|---|
| 100 | 134 | 118 | 158 |
| 120 | 161 | 141 | 189 |
| 150 | 201 | 176 | 237 |
| 180 | 241 | 212 | 284 |
| 200 | 268 | 235 | 316 |
| 220 | 295 | 259 | 347 |
| 250 | 335 | 294 | 394 |
| 280 | 375 | 329 | 442 |
| 300 | 402 | 353 | 473 |
| 350 | 469 | 412 | 552 |
| 400 | 536 | 471 | 631 |
| 450 | 604 | 529 | 710 |
| 500 | 671 | 588 | 789 |
| 600 | 805 | 706 | 947 |
| 750 | 1006 | 882 | 1183 |
At the high end, treat the flywheel columns with caution. Drivetrain loss is largely a fixed drag torque rather than a fixed share of output, so a 600 rwkw car is probably losing closer to 8–10% than 15% — see the full explanation on the whp to bhp calculator.
RWKW, ATW, AWKW and FWKW — Reading the Notation
| Notation | Means | Measured where |
|---|---|---|
| rwkw | Rear-wheel kilowatts | Driven wheels, RWD car |
| atw | At the wheels | Driven wheels, any layout — the safe generic term |
| awkw | All-wheel kilowatts | Driven wheels, AWD car |
| fwkw | Flywheel kilowatts | Estimated crankshaft, loss added back |
| rwhp | Rear-wheel horsepower | Same as rwkw, imperial units |
If a sheet says fwkw or "engine kW", the drivetrain loss has already been added back by the dyno software — usually from a coastdown measurement taken after the pull. Converting that figure again double-counts the loss and inflates the result by 15% or more.
Why Australian Dyno Numbers Often Look Conservative
A recurring complaint is that a car making, say, 300 rwkw in Australia seems to "lose" power compared with a similar build measured overseas. Usually nothing has been lost — the two measurements were taken on different equipment under different rules.
- Dyno architecture. Loaded eddy-current and water-brake dynos hold the car at steady load; inertia-only drums accelerate a known mass. They're measuring different things and rarely agree.
- Correction factor. SAE J1349, DIN, EEC and "uncorrected" produce different headline numbers from one identical run.
- Operator setup. Gear selection, tire pressure, strap tension, ambient temperature and cooling fan placement all move the result by several percent.
The reliable use of a dyno is before-and-after on the same machine, same day, same operator. A number from one workshop against a number from another — or against a brochure — isn't a like-for-like comparison, no matter how carefully you convert the units.
Turning RWKW Into Something You Can Feel
Wheel power is actually the more useful figure for judging performance, because it is what reaches the road. Divide it by mass and you get a genuine sense of pace: 200 rwkw in a 1,600 kg sedan is 125 rwkw per tonne, and the equivalent flywheel figure lands near 147 kW/tonne. Run the numbers through the kW per tonne calculator, or estimate a time with the quarter mile calculator and 0–60 mph calculator.
Related Tools
For imperial dyno sheets use whp to hp or whp to hp. To convert wheel power into kilowatts the other way round, see whp to kW, and for plain unit conversion kW to bhp. The theory behind the loss is in wheel HP vs crank HP.
Frequently Asked Questions
Rear-wheel kilowatts — power measured at the rear tires on a rolling road. It is the Australian and New Zealand equivalent of quoting wheel horsepower.
Multiply by 1.341 for wheel horsepower. For flywheel bhp, first divide by (1 − loss), then multiply by 1.341.
335 rwhp at the wheels. With a 15% loss added back, roughly 294 kW / 394 bhp at the flywheel.
A brochure kW figure is crankshaft power. RWKW is measured after the whole driveline, so it is always lower for the same car.
"At the wheels" — used for FWD and AWD cars where "rear-wheel" would be wrong. awkw is the AWD-specific form.
Divide by (1 − loss). At 15%: 200 ÷ 0.85 ≈ 235 fwkw. Multiplying by 1.15 is the common error.
Different dyno architectures and correction settings give different headline numbers from the same car. Loaded dynos common in Australia typically read more conservatively than inertia drums.
268 rwhp, roughly 235 kW at the flywheel. In a 1,600 kg sedan that's about 147 kW per tonne — genuinely quick, short of supercar territory.