Gear Ratio & Speed Calculator
Calculate top speed and RPM per gear for any transmission. Select a preset with verified gear ratios for ZF 8HP, Mercedes 722.6, 7G-Tronic and 9G-Tronic, or enter your own ratios manually. Enter your final drive ratio and tyre circumference for accurate results.
How to Use the Gear Ratio Calculator
Select a preset transmission to automatically load verified gear ratios, or choose Custom to enter your own. Enter your final drive ratio — the differential ratio, typically found on a sticker on the differential housing or in the vehicle service documentation. Enter your tyre circumference in millimetres and your engine redline RPM. The calculator shows top speed at redline per gear and displays a bar chart showing the speed range of each gear.
To find your tyre circumference use the Tyre Size Calculator on this site, or calculate it manually: outer diameter in mm multiplied by π (3.14159).
Transmission Reference
Mercedes 722.6 5G-Tronic (NAG1)
Produced from 1996 to 2020, the 722.6 is one of the most widely used automatic transmissions ever built. Two ratio sets exist — the Small NAG (W5A330) for four and six cylinder applications, and the Large NAG (W5A580, W5A400, W5A900) for V8, AMG and off-road. The 722.6 is widely used in engine swap builds and is the basis for the OFGear standalone TCU.
Mercedes 722.9 7G-Tronic (NAG2)
Introduced in 2003 as the world's first seven-speed automatic for passenger cars. Torque converter lockup in all seven gears. Gear spread of 6.016 — from 4.377 in first to 0.728 in seventh. All 722.9 transmissions share the same mechanical internals regardless of torque rating variant.
Mercedes 725.0 9G-Tronic (NAG3)
Introduced in 2013 as the world's first nine-speed automatic for premium passenger cars. Ratio spread of 9.15 — from 5.503 in first to 0.601 in ninth. Four planetary gearsets and six shift elements. Single reverse gear at 4.932. Widely used across the current Mercedes-Benz lineup and in the Aston Martin DBX.
ZF 8HP Series
The most widely used automatic transmission in modern performance vehicles, fitted by BMW, Audi, Jaguar, Land Rover, Rolls-Royce, Chrysler and others. The 8HP45 family (rated 450Nm) uses slightly different first gear ratios than the 8HP70 family (rated 700Nm), but both share the same 6th through 8th gear ratios. The 8HP90 and 8HP95 share the same ratios as the 8HP70. All ZF 8HP transmissions support standalone control via TurboLamik, CanTCU and MaxxECU.
What is final drive ratio and where do I find it?
The final drive ratio is the gear ratio in the differential. A final drive of 3.46 means the prop shaft rotates 3.46 times for every one rotation of the wheels. A numerically higher final drive gives stronger acceleration but lower top speed. The final drive ratio is typically found on a sticker on the differential housing, in the vehicle service documentation or in the original vehicle specification sheet.
How do I calculate top speed from gear ratios?
Top speed in a given gear at a given RPM = (RPM / (gear ratio × final drive)) × tyre circumference. This gives the result in mm per minute — divide by 60,000 for km/h or by 96,561 for mph. The calculator handles all of this automatically when you enter your values.