Power is torque multiplied by rotational speed, and a car's power is printed in three units: mechanical horsepower (hp), metric horsepower (PS) and kilowatts (kW). One model, the Honda Civic Type R, appears as 243 kW [330 PS] on Honda Japan's spec sheet and as 319 PS (235 kW) on Honda Malaysia's page. The two kilowatt figures sit 8 kW apart, 3.4% of Malaysia's 235 kW. That is more than a change of unit can produce: one PS is 1.37% smaller than one mechanical hp, so the same engine's PS number is about 1.39% larger than its hp number. Neither page explains the gap. The units also move where torque and power figures meet: 5,252 rpm in pound-feet and horsepower, about 7,024 rpm in newton-metres and PS, on our arithmetic.
Torque is a turning effect, a force at the end of a lever arm, measured in newton-metres (N·m). Power is how fast it does work, so it depends on engine speed in revolutions per minute (rpm).
Metric horsepower equals 735.5 watts in NIST's conversion table
Special Publication 811 of the US National Institute of Standards and Technology (NIST), in its table B.8, lists "horsepower (550 ft · lbf/s)" at 745.6999 W and the metric horsepower at 735.4988 W. NIST prints a factor in bold when it is exact, and the electric horsepower, 746 W, is the only horsepower in bold.
The published conversions are convenient, but they are rounded. The exact values can be derived from the underlying constants. The SP 811 footnotes give the pound-force, at standard gravity, as exactly 4.448 221 615 260 5 newtons. With the foot at exactly 0.3048 m, 550 foot-pounds-force a second is 745.699 87 W, by our arithmetic. Dividing 735.4988 W by the exact kilogram-force of 9.806 65 N gives 75.0000, a round 75 kilogram-force metres per second.
A 150 kW engine is therefore 201.15 hp and 203.94 PS. Singapore's Land Transport Authority prints horsepower beside kilowatts. Its COE renewal page caps Category A for fully electric cars, from the May 2022 exercise, at "110kW (147bhp)". On our arithmetic 110 kW is 147.51 hp and 149.56 PS, so the 147 is mechanical horsepower rounded down. Our COE category guide covers how the two categories work.
Pound-feet and horsepower cross at 5,252 rpm on a shared axis
One pound-force foot of torque, turned through one revolution, does 2π foot-pounds of work. A horsepower is 550 foot-pounds a second, or 33,000 a minute. Horsepower therefore equals pound-feet times rpm divided by 33,000 ÷ 2π, which is 5,252.11, and at that speed the two numbers are equal for any engine. The derivation is handbook material: Wikipedia's horsepower article gives it, citing the American Electrician's Handbook.
The crossing belongs to the units, and shows only when both curves share one numeric scale; on a chart with separate left and right axes it can fall anywhere.
Newton-metres and PS curves intersect near 7,024 rpm
Each crossover is 60 times the power unit in watts, divided by 2π times the torque unit in newton-metres. We computed five on the NIST constants.
| Torque unit | Power unit | Figures equal at (rpm) |
|---|---|---|
| lb·ft | hp | 5,252.11 |
| lb·ft | PS | 5,180.26 |
| N·m | hp | 7,120.91 |
| N·m | PS | 7,023.50 |
| N·m | kW | 9,549.30 |
The last row is the familiar motor-sizing constant, kW = N·m × rpm ÷ 9,549; the rest are the same division with different watts. They matter because both Honda pages pair N·m with PS or kW. Honda Japan quotes the Type R's peak power at 6,500 rpm, where 243 kW corresponds to 357.0 N·m against 330.4 PS, so in the sheet's own units the power number is still the smaller. In pound-feet and horsepower the same point is 263.3 lb·ft against 325.9 hp, already past the crossover.
PS heads the Malaysian spec sheet and kilowatts the Japanese one
Honda Japan's specification sheet prints 最高出力：243kW［330PS］/6,500rpm, kilowatts first, with torque as 420 N·m and 42.8 kgf·m. Honda Malaysia's spec page reverses the order under "Max Power [PS(kW)@rpm]", and its model page sets "319 PS" above the caption "HORSEPOWER". Both describe a six-speed manual with a two-litre engine, 1.995 L on the Japanese sheet and 1,996 cc on the Malaysian page.
Kilowatt figures for a single Honda model vary by 3.4% between markets
| Figure | Honda Japan | Honda Malaysia |
|---|---|---|
| Power as printed | 243 kW [330 PS] | 319 PS (235 kW) |
| Kilowatts in mechanical hp (ours) | 325.87 | 315.14 |
| Torque | 420 N·m | 420 Nm |
The 8 kW gap is 3.4% of Malaysia's 235 kW, more than twice the 1.39% a change of unit makes, while the torque figure is identical. The Japanese sheet says its main specifications are the figures in the type-designation application under Japan's Road Transport Vehicle Act (道路運送車両法). The Malaysian page names no rating standard and notes that specifications "may vary in detail". Neither says why the power figures differ, and we found no source that does.
Kilograms per horsepower clock the Type R quicker in our check
One rule of thumb divides kerb mass in kilograms by horsepower to estimate a 0–100 km/h time in seconds. We found no primary source for it. For the Malaysian Type R it gives 1,428 kg ÷ 314.64 hp (319 PS converted) = 4.54 seconds, against the 5.5 seconds Honda Malaysia publishes. That is 0.96 seconds quicker, 17.5% of Honda's figure, on one car, too small a sample to judge the rule.
Until 18 October 2026 our horsepower and torque calculator printed that rule as an indicative 0–100 time. It also opened with 200 hp and 6,000 rpm filled in, so a typed torque never changed the power: 300 N·m at 6,000 rpm showed 149.1 kW, where 188.50 kW is right. It had no PS input, and a facts heading said the curves always cross at 5,252 rpm on a tool that takes N·m and kW.
The revision committed that day starts with every field empty and solves any two of power, torque and rpm for the third. Torque 300 N·m at 6,000 rpm now returns 188.50 kW, 252.78 hp and 256.28 PS. It accepts PS, checks that hp, PS and kW typed together agree within 0.5%, computes the five crossovers above, and no longer estimates a 0–100 time.
Kilowatts form the legal unit of Singapore's electric-car road tax
For fully electric and petrol-electric cars, LTA's road-tax schedule is written in kilowatts. Its annex of March 2021, effective from 1 January 2022, bands cars by "Power Rating (kW)", each band with a six-monthly formula. Above 30 kW and up to 230 kW it is [S$250 + S$3.75(PR − 30)] × 0.782, where PR is the power rating.
At 230 kW the bracket reaches S$1,000, and the band above starts from S$1,525, both before the 0.782 factor: a step of S$525, or S$410.55 after the 0.782 factor, every six months, on our arithmetic. The rule before it split this range at 90 kW, and its upper formula also reached S$1,525 at 230 kW, so the step arrived with the merger. For those two kinds of car, the kilowatt figure decides which side of 230 kW a car falls on, whichever unit a brochure prints first.
View author profile → · Editorial policy
