Power-to-Weight Ratio Calculator — W/kg, hp/ton, kW/kg

Real-world use cases

• Compare two cars on the spec that actually matters

  A 250 hp sedan at 1600 kg and a 200 hp coupe at 1100 kg look like the faster car is obvious — until you divide. The sedan is 156 hp/ton, the coupe 182. Punch both into the tool and the lighter, lower-power car wins on power-to-weight, which is what you feel off the line. This is the number to trust when raw horsepower figures tempt you into the wrong choice.

• Set a climbing target before a sportive or race

  You weigh 72 kg and want to hold 4.5 W/kg up the queen stage climb. Enter the target and your weight in reverse mode, and the tool shows you need 324 watts at threshold. Now you have a concrete training number, not a vague goal, and you know whether this season's FTP test puts the result in reach.

• Decide whether to add power or drop weight

  Sitting at 3.8 W/kg and chasing 4.2, you can train for more watts or lose body mass. Reverse mode quantifies both paths: it might be 28 more watts, or 4.5 kg lost, or a split. Seeing the exact trade lets you pick the realistic lever instead of guessing, and the same logic works for a track car deciding between a tune and a weight strip.

• Sanity-check an EV motor swap or build

  An electric build lists a 150 kW motor and a 1250 kg curb weight. The tool converts 150 kW to about 201 hp, then reports 161 hp/ton and 120 W/kg, so you can line the build up against a known benchmark car before committing to parts. Switching the power unit to hp leaves every downstream ratio consistent.

Common pitfalls

• Mixing up metric tons and pounds. hp/ton in this tool means horsepower per metric ton (1000 kg). If you feed weight in pounds without switching the unit, the ratio is off by a factor of 2.2. Pick the weight unit first, and the labels confirm what the result is measured against.

• Forgetting bike and gear weight for cycling W/kg. On a climb, gravity acts on you plus the bike, bottles and kit — often 8 to 10 kg extra. A W/kg figured on body weight alone overstates your real climbing ratio, so for honest climb predictions add the system weight, not just your own.

• Comparing peak power against sustained power. A car's quoted peak hp and a cyclist's twenty-minute threshold are different beasts. Quoting a 6 W/kg sprint number as if it were a climbing figure flatters you badly — use the sustained power that matches the effort you actually care about.

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