Metric Horsepower to Watts

Checking a Bike's PS Figure Against the Licence Ceilings

Motorcycle adverts, dealer boards and manufacturer specs are written in PS. The rules that decide whether you may legally ride the thing are written in watts — 11 kW for A1, 35 kW for A2. Before putting a deposit down on a bike, the first job is getting the advertised horsepower onto the same scale as the licence category.

Conversion factor: 1 PS = 735.49875 W. A 47 PS twin is 47 × 735.49875 = 34 568 W, or 34.57 kW — just inside the 35 000 W A2 ceiling, with almost nothing spare.

What the Rules Actually Measure

The ceilings are set in watts

A1 stops at 11 000 W and A2 at 35 000 W. Converted, those are 14.96 PS and 47.59 PS — awkward numbers that never appear in an advert.

Weight is half the test

A2 also caps power-to-weight at 0.2 kW per kilogram, so a machine has to reach 175 kg kerb weight before it may use the full 35 kW. A1 works the same way at 0.1 kW/kg.

The 70 kW parent rule

A bike may only be restricted down to A2 if the unrestricted version makes no more than 70 000 W — about 95 PS. Anything stronger is off the list whatever kit you fit.

Two homologations, one model

Restricted and full-power variants are separate approvals with separate paperwork. The document, not the sticker on the fairing, is what an examiner or insurer reads.

Sizing Up a Bike Before You Sign for It

Whether the number comes off a classified advert, a spec sheet or a restriction kit's paperwork, the sequence is the same.

Put in the advertised PS

Enter the figure exactly as printed — 15, 45, 73.4, 119. Watts appear immediately, and a European-style decimal comma such as 73,4 is understood without changing anything.

Compare with the category ceiling

Anything at or below 11 000 W belongs to A1; up to 35 000 W is A2 territory; above that you need the full A. The result reads directly against those thresholds with no mental arithmetic.

Divide by kerb weight for the ratio test

Take the watt result, convert to kilowatts and divide by the bike's kerb mass. A 35 kW machine at 168 kg gives 0.208 kW/kg, over the 0.2 limit, so it must be held below the full power figure.

Turn the limit back into horsepower

Use the swap button (↔) to run W → PS and see the ceiling in the units the dealer speaks: 35 000 W is 47.59 PS, 11 000 W is 14.96 PS. The copy button lifts the bare number for a message or a form.

Power alone does not decide it: A1 also caps engine capacity at 125 cm³, and both categories apply the power-to-weight ratio on top of the watt limit. A bike can pass one test and fail the other.

Motorcycle Classes in PS, Watts and Licence Category

Representative machines across the range, with the manufacturer's PS figure converted exactly and the category it lands in. The two ceiling rows are the legal limits themselves, shown in both units.

Machine or limit	Output (PS)	Output (W)	Licence category
A1 power ceiling	14.96 PS	11 000 W	A1 maximum
Honda CB125R	15 PS	11 032 W	A1
Kawasaki Ninja 400	45 PS	33 097 W	A2, no restriction needed
A2 power ceiling	47.59 PS	35 000 W	A2 maximum
Yamaha MT-07	73.4 PS	53 986 W	A, restrictable to A2
Honda CB650R	95 PS	69 872 W	A, restrictable — right at the 70 kW edge
Yamaha MT-09	119 PS	87 524 W	A only
BMW S 1000 RR	210 PS	154 455 W	A only

Notice how tightly the CB650R sits: at 69 872 W it clears the 70 000 W parent-bike rule by roughly 128 W, which is why it is such a common A2 restriction candidate while the MT-09 a class above can never be one. That single row explains most of the "why can't I restrict this bike" arguments in dealer showrooms.

Handy When You Are Working Down a Dealer List

Both boxes track each other as you browse

Type over the PS value for the next bike in the listings and the watt figure follows instantly, so a shortlist of ten machines takes a single sitting.

Read the ceiling in showroom units

Reversing the direction converts 11 000 and 35 000 W into the PS numbers a salesperson will recognise, which makes the conversation shorter.

Switch to kW, the unit the rules use

The searchable dropdowns cover the full power range, so you can output kilowatts directly when filling in a restriction certificate or an insurance form.

Decimals fine enough for the weight sum

Results run to eight decimal places with thousands spaced apart, which matters when a power-to-weight calculation decides a category by a couple of hundredths.

Licence and Restriction Questions Riders Ask

What is the A2 ceiling expressed in PS?

35 000 W converts to 47.59 PS, which is why adverts talk about "47 hp bikes". A machine quoted at 47 PS is 34 568 W and legal; one quoted at 48 PS is 35 304 W and is not. There is no tolerance built into the figure, so a rounded advert is worth checking against the actual approval document.

Can any bike be restricted, or only certain models?

Only those whose unrestricted output is 70 000 W or less — roughly 95 PS. Beyond that the machine is excluded no matter how far it is throttled back, because the rule looks at the standard version rather than the state you present it in. Restriction itself is done with a throttle stop, an inlet plate, or on ride-by-wire bikes a replacement ECU map.

Why do almost all 125s make the same 15 PS?

Because 11 000 W is the ceiling and 15 PS is 11 032 W — the closest whole PS number to it. Manufacturers build to the limit and round the advertised figure up to a tidy 15, so a whole showroom of 125s ends up quoting an identical number. The differences between them are in weight, gearing and torque delivery, not output.

Does the 0.2 kW/kg rule stop a light bike using the full 35 kW?

Yes. The ratio is a second, independent test: divide the restricted power by kerb weight and it must not exceed 0.2 kW per kilogram. A 175 kg machine may use the whole 35 000 W, but a 150 kg one is capped at 30 000 W — about 40.8 PS — so lighter bikes end up deliberately over-restricted.

Why does a dyno print a lower figure than the homologation sheet?

The approval figure is crankshaft power measured on an engine test bed under controlled conditions. A rolling-road run measures at the tyre, after chain, gearbox and tyre losses that typically swallow around a tenth of the output, and it is affected by air temperature, fuel and even tyre pressure. A 73.4 PS bike reading in the high sixties on a dyno is normal — and the paperwork figure is the one that counts legally.