Quick Answer
Pick a flight controller by matching four things to your build: the mounting size, the processor class, the number of UARTs you need, and the voltage your battery will supply. After that, check for useful extras like onboard OSD and blackbox, and confirm the firmware you want to run is supported.
Start With Mounting Size
Before anything else, check that the board physically fits your frame. Most FPV flight controllers use standard mounting patterns, usually 20x20mm, 25.5x25.5mm or 30.5x30.5mm hole spacing.
A small 3-inch or whoop-class frame usually needs a 20x20mm board. Larger 5-inch and 7-inch frames commonly use 30.5x30.5mm stacks. Buying the wrong size means drilling new holes or using an adapter plate, so check your frame's spec sheet first. For a real example of one board sold in two sizes, see the Kakute H7 vs H7 Mini comparison.
Match the Processor Class to Your Plans
Flight controllers are built around different processor chips, usually labeled F4, F7 or H7. Each step up gives more processing power, more memory and often more UARTs.
- F4 is affordable and still fine for basic freestyle and racing on Betaflight.
- F7 adds more memory and handles extra features like RPM filtering with room to spare.
- H7 is the fastest option, useful for digital video systems, ArduPilot, and setups running many sensors at once.
If you are unsure which class fits your build, read our full comparison of F4 vs F7 vs H7 flight controllers for the details behind each choice.
Count Your UARTs Before You Buy
UARTs are the connections a flight controller uses to talk to other parts, like your receiver, video transmitter, GPS or telemetry radio. Each device usually needs its own UART.
Make a quick list of everything you plan to connect:
- Radio receiver
- Digital VTX or air unit (some need two UARTs)
- GPS module, if used
- Telemetry radio, if used
Add these up and buy a board with at least that many UARTs, plus one spare if you can. Running out of UARTs mid-build is a common and frustrating mistake.
Check the Voltage Input Range
Batteries come in different cell counts, and boards are rated for a voltage range. A board rated for up to 4S will not survive a 6S battery connected directly to its main pads.
Always check the maximum voltage input listed in the specs, and compare it to the battery you plan to fly. If you plan to upgrade your battery setup later, buying a board with headroom now can save a rebuild. Our guide on 4S vs 6S for FPV can help you decide on cell count first.
Look at Onboard Extras
Many modern boards bundle extra features that used to require separate parts. These are worth checking before you buy:
| Feature | Why it helps |
|---|---|
| Onboard OSD | Shows battery voltage and flight data in your goggles without extra wiring |
| Onboard blackbox flash | Lets you record and review flight data, useful for tuning your PIDs |
| Built-in current sensor | Gives a mAh-used estimate without an external sensor |
| Bluetooth | Lets you connect to the Betaflight configurator wirelessly on some boards |
Not every board needs all of these, but knowing what you are giving up on a cheaper board helps you make an informed choice.
Confirm Firmware Support
Most flight controllers can run Betaflight, but not every board supports every firmware equally well. If you plan to fly GPS missions, check that the board is listed as supported for INAV or ArduPilot before you buy. Our comparison of Betaflight vs INAV vs ArduPilot explains what each firmware is built for.
All-in-One or Separate Stack?
You will also need to decide whether to buy an all-in-one (AIO) board that includes the ESC, or a separate flight controller and ESC stack. Each has trade-offs in weight, cost and repair difficulty. Our guide on AIO vs stack flight controllers covers this decision in more detail.
New Build or Upgrade?
Your buying priorities shift a little depending on your situation. If you are building a drone from scratch, you have full freedom to pick the mounting size and UART count that fits your whole parts list. Start with the frame and work outward from there.
If you are upgrading an existing drone, your current frame and stack space set hard limits on what will fit. Measure your existing mounting holes before you buy, and check whether your current wiring harness will reach the new board's UART pads. A board that looks perfect on paper is not a good buy if it forces you to rewire the entire drone.
Pilots switching from analog to a digital video system often find this is also the moment to reconsider processor class. A digital air unit uses more UART bandwidth and, on some setups, more processing power, so it is a natural time to move up from F4 to F7 or H7 if your board is due for a change anyway.
A Simple Buying Checklist
Before you add a flight controller to your cart, run through this list:
- Does it fit my frame's mounting holes?
- Is the processor class right for my flying style and budget?
- Does it have enough UARTs for everything I want to connect?
- Is the voltage rating safe for my battery, now and later?
- Does it have the onboard extras I actually need?
- Is my firmware of choice well supported on this board?
If you answer yes to all six, you have found a solid match for your build.