Gear ratio calculator
Pick your transmission, enter the axle ratio and tire size, and see engine rpm at any speed and the speed at any rpm, in every gear. The other two tabs find an unknown axle ratio from rpm and speed, and work out the ratio of two gears from their teeth.
Inputs
Result
Every gear
| Gear | Ratio | Overall | Rpm | Speed | Rpm after shift |
|---|
Speed (mph) at each rpm
Every gear, with these tires and gears. Torque converter slip in the lower gears of an automatic makes real speeds a little lower.
The formulas
336 is a constant: 63,360 inches in a mile, divided by 60 minutes and by π (336.14 to be exact). It turns road speed and tire diameter into wheel rpm, and the gearing multiplies that up to engine rpm.
Worked example
A 700R4 or 4L60E (3.06, 1.63, 1.00, 0.70), 3.73 gears and 33 inch tires. At 70 mph in overdrive the overall ratio is 0.70 × 3.73 = 2.61, so the engine turns 70 × 2.61 × 336 ÷ 33 = 1,862 rpm. If the transmission drops out of overdrive into 3rd (1.00), the same speed takes 2,660 rpm. First gear runs out at 47 mph at 5,500 rpm, and shifting to 2nd at 5,500 lands at 2,930 rpm.
Gear ratio chart: highway rpm with overdrive
Engine rpm at 70 mph with a 0.70 overdrive top gear (700R4 / 4L60E), by axle ratio and tire diameter in inches. For a 1:1 top gear, divide by 0.70; for a 0.67 or 0.63 overdrive, multiply by 0.67 ÷ 0.70 or 0.63 ÷ 0.70.
| Axle ratio | 28 in | 30 in | 31 in | 33 in | 35 in | 37 in |
|---|---|---|---|---|---|---|
| 2.73 | 1,606 | 1,499 | 1,450 | 1,363 | 1,285 | 1,215 |
| 3.08 | 1,812 | 1,691 | 1,636 | 1,537 | 1,449 | 1,371 |
| 3.42 | 2,012 | 1,878 | 1,817 | 1,707 | 1,609 | 1,522 |
| 3.55 | 2,088 | 1,949 | 1,886 | 1,772 | 1,671 | 1,580 |
| 3.73 | 2,194 | 2,048 | 1,982 | 1,862 | 1,755 | 1,660 |
| 4.10 | 2,412 | 2,251 | 2,178 | 2,046 | 1,929 | 1,825 |
| 4.56 | 2,682 | 2,504 | 2,423 | 2,276 | 2,146 | 2,030 |
| 4.88 | 2,871 | 2,679 | 2,593 | 2,436 | 2,296 | 2,172 |
Transmission gear ratio chart
The ratios built into the calculator. Some transmissions were made with more than one ratio set, and makers round differently in the second decimal, so check the tag or spec sheet for yours.
| Transmission | 1st | 2nd | 3rd | 4th | 5th | 6th | 7th | 8th | 9th | 10th |
|---|---|---|---|---|---|---|---|---|---|---|
| GM 700R4 / 4L60E (4-speed auto) | 3.06 | 1.63 | 1.00 | 0.70 | ||||||
| GM 4L80E (4-speed auto) | 2.48 | 1.48 | 1.00 | 0.75 | ||||||
| GM 6L80E (6-speed auto) | 4.03 | 2.36 | 1.53 | 1.15 | 0.85 | 0.67 | ||||
| GM TH350 (3-speed auto) | 2.52 | 1.52 | 1.00 | |||||||
| GM TH400 (3-speed auto) | 2.48 | 1.48 | 1.00 | |||||||
| GM 200-4R (4-speed auto) | 2.74 | 1.57 | 1.00 | 0.67 | ||||||
| Powerglide (2-speed auto) | 1.76 | 1.00 | ||||||||
| Ford 10R80 (10-speed auto) | 4.70 | 2.99 | 2.15 | 1.80 | 1.52 | 1.28 | 1.00 | 0.85 | 0.69 | 0.64 |
| Jeep JL 8-speed auto (850RE) | 4.71 | 3.13 | 2.10 | 1.67 | 1.28 | 1.00 | 0.84 | 0.67 | ||
| Jeep JL 6-speed manual (D478) | 5.13 | 2.63 | 1.53 | 1.00 | 0.81 | 0.72 | ||||
| Tremec T56 Magnum, close ratio | 2.66 | 1.78 | 1.30 | 1.00 | 0.80 | 0.63 | ||||
| Tremec T56 Magnum, wide ratio | 2.97 | 2.10 | 1.46 | 1.00 | 0.80 | 0.63 | ||||
| Tremec TKX, 3.27 first | 3.27 | 1.98 | 1.34 | 1.00 | 0.72 | |||||
| Tremec TKX, 2.87 first | 2.87 | 1.89 | 1.28 | 1.00 | 0.81 | |||||
| Ford T5 (Mustang 5-speed) | 2.95 | 1.94 | 1.34 | 1.00 | 0.63 |
Sources: Dieselhub (10R80, 700R4), 700R4 Transmission HQ (GM automatics), Gearstar (6L80E), Tremec ratio tables via Malwood (T56 Magnum, TKX, T5), Quadratec (Jeep JL).
What a gear ratio means
A ratio is how many turns the input makes for one turn of the output. With 3.73 gears, the driveshaft turns 3.73 times for every turn of the wheels. Torque is multiplied by the same factor (less a few percent lost to friction), and speed is divided by it.
For two gears in mesh, the ratio is the driven gear’s teeth divided by the driving gear’s. A ring gear with 41 teeth turned by an 11-tooth pinion is 41 ÷ 11 = 3.727, sold as 3.73. In a gear train, multiply the ratio of each pair; idler gears in between change the direction, not the ratio.
“Higher” and “lower” gears
The words run backwards from the numbers. A numerically higher ratio, such as 4.10 instead of 3.55, is called a lower (or “shorter”) gear: more torque at the wheels and quicker acceleration, but more engine rpm at a given speed. A numerically lower ratio is a “taller” gear: fewer rpm on the highway and less pull. Bigger tires make any ratio act taller, which is why lifted trucks are often re-geared; the tire size calculator works out the ratio that brings the original rpm back.
How to find your axle ratio
- Look for a tag or code. Many axles have a metal tag on a cover bolt with the ratio stamped on it, and many trucks list the axle code on the door sticker, glovebox sticker or build sheet, which a dealer can decode from the VIN.
- Count the turns. With the vehicle safely on stands, transmission in neutral, mark the driveshaft and a tire. If both wheels turn together, turn the tire once and count the driveshaft turns: that is the ratio. With one wheel up on an open differential, turn the tire twice instead.
- Use rpm and speed. Hold a steady speed on the flat in a gear you know, with the converter locked, read the rpm and the GPS speed, and use the “Find my axle ratio” tab. For example, 2,580 rpm at 65 mph in a 1:1 gear on 31.6 in tires works out at 3.73, so 3.73.
Crawl ratio
Crawl ratio is the overall ratio in the lowest gear with the transfer case in low range: first gear × low range × axle ratio. It tells off-roaders how slowly the vehicle can creep with the engine at idle, and how much the engine’s torque is multiplied. A Jeep JL with the 8-speed automatic (4.71 first), the 4.0 Rock-Trac low range and 4.10 axles has 4.71 × 4.0 × 4.10 = 77.2:1; with the 6-speed manual (5.13 first) it is 84.1:1. With the 2.72 Command-Trac and 3.45 axles, the automatic is at 44.2:1.
Questions
How do you calculate gear ratio?
Divide the number of teeth on the driven (output) gear by the number on the driving (input) gear. 41 teeth driven by 11 is 41 ÷ 11 = 3.73:1. For a vehicle, multiply the transmission gear by the axle ratio (and the transfer case ratio, if it is in low range) to get the overall ratio.
How do I calculate rpm from gear ratio and speed?
Engine rpm = mph × axle ratio × transmission gear × 336 ÷ tire diameter in inches. 70 mph with 3.73 gears, a 0.70 overdrive and 33 inch tires is 70 × 3.73 × 0.70 × 336 ÷ 33 = about 1,862 rpm.
How do I calculate speed from rpm and gear ratio?
Speed in mph = rpm × tire diameter ÷ (axle ratio × transmission gear × 336). With 3.73 gears, a 3.06 first gear and 33 inch tires, 5,500 rpm in first is about 47 mph.
How do I find out what gear ratio my rear end has?
Check for a tag on the axle cover, or the axle code on the door or glovebox sticker. Otherwise, jack up the vehicle, mark the driveshaft and tire, turn the tire one turn (two turns with one wheel up on an open differential) and count driveshaft turns. Or hold a steady speed in a known gear and use rpm and GPS speed: 2,580 rpm at 65 mph in 1:1 on 31.6 in tires is 3.73, a 3.73.
Is a 3.73 or 4.10 gear ratio better?
Neither is better in general. 4.10 is about 10% shorter: more pull for towing, off-road and bigger tires, but 10% more rpm on the highway. 3.73 cruises at lower rpm. Work out the rpm at your usual cruising speed with your tires and transmission and compare.
What is a good crawl ratio?
It depends on the use; higher numbers mean slower, more controlled crawling. As a reference, a Jeep JL with the 8-speed automatic, 4.0 Rock-Trac and 4.10 axles calculates to 77.2:1, and with the 2.72 Command-Trac and 3.45 axles 44.2:1.
Does tire size change the gear ratio?
Not the ratio itself, but the effect is the same. A taller tire covers more ground per turn, so the engine turns fewer rpm at a given speed, as if the axle ratio were numerically lower by the same percentage.
What does a 0.70 overdrive mean?
In that gear the output shaft turns faster than the engine: 1 ÷ 0.70 = 1.43 turns for every engine turn. It cuts engine rpm by 30% compared with a 1:1 gear at the same speed.