Performance Tools
RC Boat Speed Calculator
These formulas are for an estimate only. If you like to play with numbers, these tools can be a major help in starting a new boat building project.
Please keep in mind you can plug any number you like into the fields — it doesn't mean it will work! You have to have a basic understanding of the limits of your parts. For example, a 300 gram 2000kv motor will spin a 45mm prop just fine in most 25–30" racing hulls on 14 volts. But that same motor will burn up itself or the ESC in a 50" boat.
It's pretty simple to use the formulas: anywhere a field is shaded yellow, change the value to a number. Letters or spaces in a field will cause an error. One of the calculators we have particular interest in is Estimate the Top Speed of a Prop — it's amazing to see how much speed our hulls and props are wasting.
Quick Speed Estimate
Enter your setup's KV, voltage, and prop pitch for a fast top-speed estimate.
Common Battery Voltages
Nominal vs. fully-charged voltage by cell count, for reference.
| Pack | Nominal V | Charged V |
|---|---|---|
| 2S LiPo | 7.4 V | 8.4 V |
| 3S LiPo | 11.1 V | 12.6 V |
| 4S LiPo | 14.8 V | 16.8 V |
| 5S LiPo | 18.5 V | 21.0 V |
| 6S LiPo | 22.2 V | 25.2 V |
| 8S LiPo | 29.6 V | 33.6 V |
Do The Math
Advanced Calculators
Anywhere a field is shaded yellow you can plug in your own numbers — letters or blank fields will break the math. Click outside the field to recalculate.
Detailed Speed Estimate (Motor / Battery / Prop / Gearing)
The full breakdown — same math as the quick calculator above, but lets you enter motor efficiency, cell count, and pinion/spur gearing separately instead of a single combined voltage and ratio.
Motor
Battery Pack
Propeller
Gear Box (1:1 if direct drive)
Inches / Millimeters / Centimeters
Click out of a field to convert.
Estimate Amp Draw
From battery capacity and run time.
Estimate Runtime
From cell capacity and discharge current.
NiMH & NiCd Voltage / Power Under Load
Pack voltage and power output under load.
Estimate Speed With a Stopwatch
Time your boat between two known points.
Estimate the Top Speed of a Prop
On most Octura props the first two digits give the pitch — e.g. an X438 is 1.4 pitch, 38mm diameter.