Torque & Drivetrain Calculators
Calculate torque from RPM, horsepower, or engine size, work out final drive, gear, and sprocket ratios, check drivetrain and gearbox losses, and torque down gaskets, alternators, and stall converters to spec.
From Crank to Wheel: How Torque Multiplies Through the Drivetrain
An engine’s torque number on a spec sheet isn’t what reaches the ground. It gets multiplied twice — once by the transmission’s gear ratio, once by the final drive — then reduced by friction along the way. Start with RPM to Torque to pull torque out of a horsepower and RPM reading, or Flywheel Torque for the raw output at the crank before anything downstream touches it.
From there, wheel torque is engine torque times gear ratio times final drive ratio, minus whatever the gearbox, differential, and bearings absorb. Wheel Torque runs that full chain, Crank to Wheel HP does the same for power instead of torque, and Drivetrain Loss isolates just the percentage lost in between — typically around 10-15% for a manual layout and noticeably more for automatics or all-wheel drive.
Matching Gear and Sprocket Ratios to How You Drive
A gear ratio is just driven teeth divided by driver teeth, but that one number decides whether a vehicle pulls hard or cruises easy. Final Drive Ratio and RPM Gear Ratio tie a specific ratio to engine RPM at road speed, which is the same math a rear axle swap or a taller cruising gear runs on.
Motorcycles use the identical idea with chain and sprockets: rear tooth count divided by front tooth count. Drop a tooth off the front sprocket and the ratio climbs more than dropping several off the rear, because the front sprocket is so much smaller — that’s why Motorcycle Sprocket Ratio treats front and rear changes differently rather than averaging them.
Once you’ve settled on a ratio, Sprocket Speed converts it straight into wheel speed at a given engine RPM. None of this accounts for what the gearbox itself eats internally, which is what Gearbox Efficiency is for — every gear mesh gives up a few percent to friction, and a multi-stage box compounds it.
Comparing Torque Across Engines and Vehicles
Raw torque numbers don’t compare fairly across different vehicles, the same way raw horsepower doesn’t. Torque To Weight Ratio and Torque Per Ton both normalize torque against vehicle mass, which is the more honest way to judge how hard something pulls, especially for towing and hauling comparisons rather than straight-line speed.
If you’re working from displacement instead of a dyno sheet, Cc To Torque gives a rough stock-engine estimate. And if you’re chasing why a motor feels weaker after mileage or a modification, Torque Loss quantifies the drop between two readings instead of leaving it to feel.
Torque Converters and Stall Speed
An automatic transmission’s torque converter has its own torque behavior, separate from the engine bolted to it. Stall Torque covers the torque the converter produces at stall, before the vehicle starts moving.
Converters are rated by a K-factor — stall RPM divided by the square root of engine torque — so a builder can compare converters independent of whichever engine they end up paired with. Stall Converter K Factor runs that formula directly, which is the same rating system stamped on OEM converter tags.
Torque Specs for Accessories and Fasteners
Not every calculator here is about acceleration. Alternator Pulley Ratio compares crank pulley size to alternator pulley size to find how much faster the alternator spins than the engine, which decides how well it charges at idle. Alternator Torque covers the drag that spinning it places back on the engine.
Gasket Torque works through fastener torque sequencing — exact specs vary by engine and bolt type, so it’s a starting point alongside the factory manual, not a replacement for it. And Output Shaft Speed ties transmission output RPM to actual wheel speed once the final drive and tire size are known.
Frequently Asked Questions
How do you calculate wheel torque from engine torque?
Multiply engine torque by the transmission’s gear ratio, then by the final drive ratio. That gives ideal wheel torque; subtract drivetrain loss for a realistic number.
How much torque does a drivetrain actually lose?
A manual gearbox and axle typically keep around 90% of engine torque, so roughly 10% is lost to friction. Automatics and all-wheel-drive systems usually lose more, often landing in the 15-20% range.
What counts as a good torque-to-weight ratio?
There’s no fixed target — it’s a comparison metric, not a pass/fail number. A higher ratio means more pulling force per pound of vehicle, which is why it’s most useful when comparing two specific vehicles side by side rather than judging one in isolation.
What is torque converter K-factor?
K-factor is stall RPM divided by the square root of engine torque. It lets a torque converter be rated on its own, independent of which engine it’s paired with, which is why it’s printed on the converter itself.
How do you work out a motorcycle’s sprocket ratio?
Divide the rear sprocket’s tooth count by the front sprocket’s tooth count. A higher ratio multiplies torque more but lowers top speed at a given engine RPM; a lower ratio does the opposite.
Why does gearbox efficiency matter if the gear ratio is already known?
The ratio tells you how much torque should be multiplied in theory. Efficiency tells you how much of that actually survives the trip through the gears, since every mesh loses a small percentage to friction — and a multi-stage gearbox stacks those losses.