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Free Tool

RC Parts Matcher

You already own some of it. Enter the parts you have — a motor, a prop, an ESC, a battery, any three of them — and this works out the ones you don’t, with the current, watts, flight time and the warnings that save a controller.

Quick answer

Fill in any three of motor Kv, battery cells, propeller size and ESC rating. The rest is arithmetic: a propeller’s power demand rises with the cube of rpm, the fourth power of diameter and the first power of pitch, and current is that power divided by pack voltage. Everything else — ESC size, C rating, flight time — follows from there.

Motor
Printed on the motor or its listing. Leave blank to solve for it.
Propeller
A “10x4.7” prop is 10 diameter, 4.7 pitch. Pitch alone can be left blank.
Speed control
The continuous rating printed on the label.
Battery
Optional — the plane
Weight unlocks watts per pound. Flight time sizes the pack.
Common Questions

Matching a power system, answered

Size the ESC to the current the propeller actually pulls, not to the motor's name. Current is power divided by pack voltage, and a propeller's power demand rises with the cube of rpm, the fourth power of diameter and the first power of pitch. Work that out for your Kv, cell count and prop, then choose a controller rated about a third above it so the continuous draw sits near 75% of the rating. The matcher does the arithmetic and rounds to a size you can buy.
The ESC is usually the ceiling. Its amp rating multiplied by your pack voltage is the most power the system will pass, so the right prop is the one that loads the motor to about three quarters of that. Because power scales with diameter to the fourth power, one inch of extra diameter raises the demand by roughly 46% on a 10-inch prop, which is the quickest way to cook a controller.
Because the two enter the power relation with different exponents. Power rises with the fourth power of diameter but only the first power of pitch. On a 10-inch prop, going up one inch of diameter asks for about 46% more power, while going up one inch of pitch asks for about 21%. If a setup is running hot, take diameter off before you touch pitch.
Current goes up with the square of voltage, not in step with it. Going from 3S to 4S raises the pack voltage by a third, raises power by 1.33 cubed, which is 2.37 times, and raises current by 1.78 times. That is why adding a cell without changing the prop is the most common way to destroy an ESC.
Capacity divided by current gives the time at that current. Nobody flies at full throttle throughout, so a reasonable estimate uses about half the full-throttle draw as the average, and you should plan to land with roughly 20% of the pack still in it. A 1300 mAh pack on a setup pulling 12 amps wide open is about five minutes flat out, or ten minutes of normal flying.
A trainer flies comfortably on 50 to 70 watts per pound. Sport and aerobatic models want 100 or more, and unlimited aerobatics start around 200. Below about 50 a plane will still fly if the wing is large and the airframe light, but it will not climb out of a mistake.
How this works

The two relationships behind every answer

There is no table of blessed combinations here. Every number is solved from what you typed, using two relationships that hold for any electric setup.

A propeller’s power demand. Power rises with the cube of rpm, the fourth power of diameter, and the first power of pitch. That single fact explains most burnt ESCs: one inch of extra diameter on a 10-inch prop asks for about 46% more power at the same rpm, while an inch of extra pitch asks for about 21%.

A brushless motor’s speed. Unloaded it turns Kv times the pack voltage. With a propeller on it, expect roughly 70% of that. Add a cell without changing the prop and the rpm rises by the voltage ratio, power by its cube, and current by its square — which is why 3S to 4S nearly doubles the amps.

From those two, current is power over voltage, ESC size is current with headroom, C rating is current over capacity in amp-hours, and duration is capacity over current. Static thrust comes from momentum theory, derated to what a real propeller achieves standing still.

How accurate is it? The constants were checked against three setups with published numbers before this went live: a Spektrum Avian 5065 at its rated 1200 watts solves to the 17-inch prop Spektrum recommends, Eric’s ER Moth solves to the 5-inch prop it actually flies, and an APC 10x4.7 at 8000 rpm solves to within a few watts of APC’s own figure. Treat the answers as the right size and the right ballpark — a wattmeter on your own bench is still the final word.

Next

Where this fits in the build

This tool is for when you already own something. If you are starting from nothing, the other two are quicker.

Don't own anything yet → matched sets by wingspan Starting from scratch → Checklist Builder Designing the airframe → Airplane Designer Wiring it → Wiring Designer CG and wing loading → Calculators Setups that actually flew →
From the shop

Made here for this job

Small parts from my own bench that make the wiring side of a build cleaner.

Everything for sale →
Assorted heat-shrink servo lead labelsServo Lead Heat-Shrink LabelsAIL, ELE, RUD, THRO and the rest, shrunk onto the lead so the receiver bay reads itself. Four packs.from $19.99See the label kit → A black safety lock fitted around a joined servo connectionServo Connector Safety LocksFifty locks that fit around a joined servo connection so an extension out in a wing stays plugged in.$14.99See the locks → A red and green XT60 battery status capXT60 Battery Status CapsGreen end out: charged and ready. Red end out: flown. Twelve caps, so every pack in the box tells you.$11.99See the caps →