The conversions car people actually need - torque, power, pressure, speed, weight - all live, all on one page. Type in either box.
Automotive specifications are a constant collision of two measurement systems. A German manufacturer quotes power in PS and torque in Nm, an American magazine quotes HP and lb-ft, an EV spec sheet lists kW, and your boost gauge might read bar while the build thread next to it talks PSI. Knowing which unit a number is in - and how to move between them - is the difference between comparing cars correctly and being fooled by a figure that only looks bigger. Below are the conversions that matter most in the garage, why each unit exists, and when you'll actually run into it.
European spec sheets quote PS (metric horsepower, "Pferdestärke") which is ~1.4% smaller than the US/UK HP - a "510 PS" M5 is 503 HP. Kilowatts (kW) are the SI unit and the figure on European registration papers and EV specs. Everything converts cleanly through kilowatts: 1 kW = 1.341 HP = 1.360 PS. When you compare a German car rated in PS against an American car rated in HP, convert both to the same unit first or you'll overstate the metric car by about 1.4%.
Torque is twisting force, and the unit you see depends on where the car was engineered. European torque figures in Nm look dramatically bigger than lb-ft (650 Nm = 479 lb-ft) simply because a newton-metre is a smaller unit than a pound-foot. Multiply Nm by 0.7376 for lb-ft, or lb-ft by 1.3558 for Nm. This shows up constantly when reading torque specs, wheel-bolt torque values, and dyno graphs from different markets.
1 bar ≈ 14.5 PSI, and since 1 bar = 100 kPa, then 100 kPa ≈ 14.5 PSI too. European boost gauges and turbo discussions use bar (1.5 bar ≈ 21.8 PSI of boost); tire-pressure placards in much of the world list bar or kPa, while US gauges read PSI (2.5 bar ≈ 36 PSI). Get this one wrong on tire pressure and you're either riding on rocks or rolling the sidewalls.
Speed and speedometer markings split along the same lines: 1 mph = 1.609 km/h. A 155 mph limiter is the famous 250 km/h "gentlemen's agreement" figure; 60 mph is about 97 km/h, and 100 km/h - the metric 0-100 benchmark - is about 62 mph, which is why a metric 0-100 km/h time is always a touch slower than the same car's 0-60 mph.
Wheel and tire dimensions mix units in a single size: tire section width is in millimeters, wheel diameter in inches (1 inch = 25.4 mm). Rotor sizes, brake pad dimensions, and ride-height drops are usually metric in the spec but discussed in inches by enthusiasts. Multiply inches by 25.4 for mm, or divide mm by 25.4 for inches.
Unlike everything else here, °C ↔ °F isn't a simple multiplier: °F = °C × 1.8 + 32 (and °C = (°F − 32) ÷ 1.8). The scales have different zero points, so you can't just scale the number. Useful references: 100°C / 212°F (coolant boiling unpressurized), 90°C / 194°F (typical oil temp), and ~120°C / 250°F (oil temp where you should back off).
You're cross-shopping a European coupe rated 510 PS and 650 Nm against an American car listed at 495 HP and 470 lb-ft. To compare them fairly, put everything in one system. Convert the European figures:
So the "510 PS" car is really making about 503 HP and 479 lb-ft - genuinely a bit stronger than the 495 HP / 470 lb-ft American car, but the gap is far smaller than the headline numbers suggest. Now add boost context: if the European car runs 1.5 bar and a tuner quotes the American car at 20 PSI, convert one side - 1.5 bar × 14.5 ≈ 21.8 PSI - and you can see they're boosting to roughly similar levels. Same idea for tire pressure: a placard reading 2.4 bar is 2.4 × 14.5 ≈ 35 PSI on your shop gauge.
Multiply kilowatts by 1.341 to get HP, or divide HP by 1.341 to get kW. So 300 kW is about 402 HP, and 400 HP is about 298 kW. Kilowatts are the SI unit used on European registration documents and EV specs, while HP (mechanical horsepower) is standard in the US and UK.
PS is metric horsepower (Pferdestärke), the figure most European manufacturers quote, and it is about 1.4% smaller than mechanical HP. A car rated 510 PS makes about 503 HP. Both convert cleanly through kilowatts: 1 kW = 1.341 HP = 1.360 PS.
Multiply newton-metres by 0.7376 to get pound-feet, or multiply lb-ft by 1.3558 to get Nm. For example 650 Nm equals about 479 lb-ft. European torque figures in Nm look much larger than the same torque in lb-ft, which is why a metric spec sheet can seem more impressive than it is.
One bar is about 14.5 PSI, and 100 kPa is also about 14.5 PSI (1 bar = 100 kPa). So 1.5 bar of boost is roughly 21.8 PSI, and a 2.5 bar tire pressure is about 36 PSI. European boost gauges and tire placards usually read bar or kPa.
Temperature scales have different zero points, so the conversion includes an offset: °F = °C × 1.8 + 32, and °C = (°F − 32) ÷ 1.8. Unlike torque or power, you cannot just scale the number. Handy references: 100°C equals 212°F (water boiling unpressurized) and 0°C equals 32°F (freezing).
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