Aisha K.
Mar 12, 2026
Clean layout and the results update instantly. Exactly what I needed for a quick planning check.
Unit Converters
Gear Ratio to Speed Calculator
mph = (rpm / ratio) × π × D_in × 60 / 63360.
mph ≈ RPM / ratio × tire circumference × 60 / 63,360. Overall ratio is gear × final drive × (transfer case). Torque converter slip in autos is extra. Use the tire-size page for diameter.
Drivetrain
Road speed
48.1 mph
77.3 km/h.
Plain-English guide
Terms & how it works
Confused by a field? Read the short definitions here while you use the tool.
Engine RPM
The “Engine RPM” value used in this tool’s formula. Adjust it to see results update live.
Overall gear ratio
The “Overall gear ratio” value used in this tool’s formula. Adjust it to see results update live.
Tire diameter (in)
The “Tire diameter (in)” value used in this tool’s formula. Adjust it to see results update live.
How this calculator works
mph ≈ RPM / ratio × tire circumference × 60 / 63,360. Overall ratio is gear × final drive × (transfer case). Torque converter slip in autos is extra. Use the tire-size page for diameter. mph = (rpm / ratio) × π × D_in × 60 / 63360. Example: 2500 rpm, 4.10 overall, 26.5 in tire → about 48 mph.
mph = (rpm / ratio) × π × D_in × 60 / 63360.
Example: 2500 rpm, 4.10 overall, 26.5 in tire → about 48 mph.
When to use this Gear Ratio to Speed
Common use cases
- mph ≈ RPM / ratio × tire circumference × 60 / 63,360. Overall ratio is gear × final drive × (transfer case). Torque converter slip in autos is extra. Use the tire-size page for diameter.
- Sanity-check with this case: 2500 rpm, 4.10 overall, 26.5 in tire → about 48 mph.
- The relationship is: mph = (rpm / ratio) × π × D_in × 60 / 63360.
Localized examples
- Unit Converters: the example on this page uses the same formula as the widget.
What you get
- Fields: Engine RPM, Overall gear ratio, Tire diameter (in)
- mph = (rpm / ratio) × π × D_in × 60 / 63360.
- Example on the page: 2500 rpm, 4.10 overall, 26.5 in tire → about 48 mph.
How to Convert Gear Ratio to Speed Step-by-Step
- 1Enter Engine RPM, Overall gear ratio, Tire diameter (in). Use the values you have, not a catalog average, unless that is all you know.
- 2mph = (rpm / ratio) × π × D_in × 60 / 63360.
- 3Worked case: 2500 rpm, 4.10 overall, 26.5 in tire → about 48 mph.
- 4Check which dictionary the other person is using — US or UK, decimal or 1,024 — then trust the number.
Governing formula
mph = (rpm / ratio) × π × D_in × 60 / 63360.
2500 rpm, 4.10 overall, 26.5 in tire → about 48 mph.
Example: set Engine RPM = 2,500, Overall gear ratio = 4.1, Tire diameter (in) = 26.5, then read the result.
Variable definitions
- value
Engine RPM
The “Engine RPM” field. Default 2500; typical range 500–8000.
- ratio
Overall gear ratio
The “Overall gear ratio” field. Default 4.1; typical range 0.5–20.
- tireIn
Tire diameter (in)
The “Tire diameter (in)” field. Default 26.5; typical range 12–40.
- The conversion (mph = (rpm / ratio) × π × D_in × 60 / 63360.) does not pick US vs UK gallons, SI vs binary megabytes, or Mach at altitude for you. Read the footnote on the page.
- Nothing here is uploaded for the calculation itself.
Frequently Asked Questions
3rd gear × axle. Do not use only the axle if you are not in 1:1.
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Reviews & Ratings
See what others think about this tool, then leave your own rating to help improve CalculioHub.
4.8
out of 5.0
4 reviews
Daniel R.
Feb 28, 2026
Very usable on mobile. Would love a save/export option later, but the math feels solid.
Priya S.
Feb 3, 2026
The FAQ section answered my questions before I even had to search. Smooth dark mode too.
Marcus L.
Jan 19, 2026
Simple inputs, clear outputs. This replaced three bookmarks I used to juggle.
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