Gear Ratio Speed Calculator

The gear ratio speed calculator will determine the speed ratio of your two-gear system, while explaining the concepts of gear ratios along the way.

Output speed1,000 rpm16.6667 revolutions a second

Gear ratio3:145 driven teeth ÷ 15 driving

TypeReductionslower and stronger at the output

Output torque349.2 N·m257.557 lbf·ft

Torque multiplication2.91×the ratio less 3% lost to friction

Input power37.6991 kW

Output power36.5681 kWpower is what a gearbox cannot increase — only redistribute between torque and speed

Power lost as heat1.131 kW

Hunting ratio?no — common factor 15the same tooth pairs keep meeting, concentrating wear — designers usually avoid a common factor

Revolutions of the driving gear per output turn3

The formula

ratio = driven teeth ÷ driving teeth; torque and speed trade inversely

Torque and speed, never both

A gear ratio is the driven tooth count divided by the driving one. Above one it is a reduction: the output turns more slowly and with proportionally more torque. Below one it is an overdrive, trading torque for speed. Power — torque times angular velocity — is what a gearbox cannot increase; it can only redistribute what it is given, minus a few percent to friction.

The hunting-ratio check is a real design consideration. If the two tooth counts share a common factor, the same pairs of teeth meet over and over, so any manufacturing error or hard spot wears one pair repeatedly. Coprime counts make every tooth eventually meet every other tooth, spreading wear evenly — which is why you often see 15 and 46 rather than 15 and 45.

Multiple stages multiply their ratios and their losses. Two 97% stages give 94% overall, which is why a deep reduction is usually built as a few moderate stages rather than one extreme one.