RC Car Scale Speed Calculator
Convert your RC car’s real speed into its full-size scale speed for any scale (1:5 to 1:87). Enter a measured speed, time a run over a known distance, or estimate top speed from motor kV, battery, gearing and tyre size. Results in mph, km/h and m/s, with the realistic-looking (Froude) speed, a scale chart and a pinion gearing table.
How it works
Scale speed = real speed × N (for a 1 : N model) · Timed run: real speed = distance ÷ time · Motor: speed = kV × volts ÷ (spur ÷ pinion × internal ratio) × π × tyre diameter × efficiency · Froude (realistic-looking) speed = real speed × √N
Scale speed answers a hobbyist favourite: if this model were blown up to full size, how fast would it look like it was going? The model is 1/N the size of the real thing, so each second it covers 1/N of the equivalent full-size distance, and multiplying the real speed by N gives the scale speed. That is why a modest 20 mph on a 1:10 car scales to a supercar-like 200 mph. The calculator takes the real speed three ways: a measured figure from GPS or radar, a timed run between two marks, or an estimate from the motor’s kV, battery voltage, gearing and tyre diameter. The motor estimate is the usual RC top-speed formula, with an efficiency factor because a loaded car never reaches the no-load figure. There is also a second, more realistic comparison. Film-miniature makers scale speed by the square root of N (Froude scaling), because that keeps jumps, bounces and acceleration looking natural on camera; on that basis the same 1:10 car at 20 mph moves like a full-size car at about 63 mph. A table compares common scales, and in motor mode a gearing chart shows the top speed for each pinion size.
Worked example
A 1:10 scale RC car clocked at a real 20 mph has a scale speed of 20 × 10 = 200 mph (321.9 km/h), and a Froude speed of 20 × √10 ≈ 63.2 mph. With a 3,300 kV motor on 2S LiPo (7.4 V), an 18-tooth pinion, a 72-tooth spur, a 2.6 internal ratio and 110 mm tyres, the motor spins 24,420 rpm, the final drive is 10.4 : 1, and the no-load speed is about 30.3 mph. At 85% efficiency that is about 25.7 mph real, or 257 mph at scale.
Sources: Froude number and similitude (Wikipedia) · Motor constants: kV (Wikipedia)
Frequently asked questions
What is scale speed?
It is the speed a full-size version of your model would appear to travel, found by multiplying the real speed by the scale factor. It expresses the model’s pace in real-world terms and is a way to compare RC performance, not a measure of actual ground speed.
How do I measure the real speed?
Use a radar gun or GPS speed logger, or time the car over a known distance: choose Timed run, enter the distance between two marks and the time. A 30 m straight covered in 3 s is 10 m/s, about 22.4 mph.
How fast will my RC car go with this motor and gearing?
Choose Motor & gearing and enter the motor kV, battery cells, pinion and spur teeth, the internal ratio and the tyre diameter. The calculator gives the no-load speed and a realistic top speed (about 85% of no-load), plus a chart of top speed for nearby pinion sizes.
Does a smaller scale give a higher scale speed?
Yes, for the same real speed. A 1:24 car at 20 mph scales to 480 mph, against 200 mph for a 1:10 car, because the smaller model represents a proportionally larger full-size vehicle covering more scale distance per second.
What is the Froude or realistic-looking speed?
When a model moves, gravity does not scale, so a car driven at true scale speed looks frantic on video. Miniature-effects crews film or drive at real speed × √N to make motion look natural. For a 1:10 car that is about 3.2 times the real speed, not 10 times.
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This calculator is for educational purposes. Double-check important results before acting on them.