1. Why use an FPV calculator?

Every component changes the rest of the system. High KV on 6S can increase current and heat; a low-C battery can sag under throttle; excess weight makes the drone sluggish and shortens flight time.

KV and voltage

Match motor KV to cell count and propeller load. Always confirm the motor manufacturer's data.

Battery C rating

Insufficient current delivery creates sag, weak acceleration and faster voltage drop.

Weight

More weight lowers the thrust reserve and changes how the craft brakes and responds.

2. Thrust-to-weight ratio

For a quad: Thrust Ratio = (maximum thrust of one motor × 4) / all-up weight. Include battery, camera, straps and every part that flies.

(motor thrust in g x 4) / drone weight in g = Thrust Ratio
RatioFeelTypical use
2:1-3:1Minimum reserveCinewhoop, cargo and long range
4:1-6:1Balanced controlFreestyle and everyday flying
8:1-10:1+Very sharp accelerationRacing builds
Example:A 1500g motor and 600g take-off weight gives 1500 × 4 / 600 = 10:1. That is a large reserve, not a reason to fly at full throttle constantly.

3. Current load and ESC headroom

Estimate total peak current as peak current of one motor × 4. The ESC should have at least 20-30% headroom instead of matching the peak exactly.

ESC target >= (peak current per motor x 4) x 1.2 to 1.3
Example: 40A per motor40 × 4 = 160A total. A 50-60A per-channel 4-in-1 ESC may be a starting point, but check real manufacturer tests.
Do not forget the capacitorFor 6S use a suitable Low-ESR capacitor, often 35V or 50V, with correct polarity.

4. Flight-time estimate

Rough formula: minutes = (capacity mAh × 0.8 / (average current A × 1000)) × 60. The 0.8 factor keeps about 20% reserve.

((capacity mAh x 0.8) / (average current A x 1000)) x 60 = minutes

For a 1300mAh pack at 20A average, the estimate is about 3.1 minutes. Wind, temperature, battery age, flight style and voltage alarms change the real result.

5. Basic 5-inch reference values

Parameter4S build6S build
Nominal battery voltage14.8V22.2V
Motor KV guide2400-2750KV1750-1950KV
Peak current per motorabout 45-55Aabout 35-45A
ESC guide45-50A50-60A
Battery capacity1300-1550mAh1100-1400mAh

These are starting points, not guarantees. Verify the exact motor, propeller, weight and manufacturer thrust table.

6. Other useful tools

eCalc / xcopterCalc

Detailed modelling of thrust, aerodynamics, heat, propeller efficiency and energy use.

Oscar Liang / FPV Calculators

Convenient spreadsheets for KV, weight and flight-time estimates.

Betaflight KV Scaling

Motor output limit can reduce the effective output of a high-KV motor, but it does not replace current and temperature checks.

7. Compatibility checklist

  • Battery voltage matches motor KV and ESC limits.
  • Peak motor current leaves 20-30% ESC headroom.
  • The Low-ESR capacitor is rated for the selected cell count.
  • Thrust-to-weight is at least 4:1 for comfortable freestyle.
  • All-up weight includes battery, camera, straps and small parts.
  • The prop fits the frame and the motor has the correct mounting pattern.
  • The calculation is checked against the exact motor thrust table.
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