What formula does this calculator use?

It applies actuator-disk theory (momentum theory) from rotary-wing aerodynamics. Ideal hover power is P_ideal = sqrt(T^3 / (2 * rho * A_total)), where T is thrust (= weight for hover), rho is air density at the given altitude using the ISA troposphere model, and A_total is the summed disk area of all rotors. Real power adds a figure of merit (FM ≈ 0.65–0.82) that accounts for non-ideal flow: P_hover = P_ideal / FM. Flight time follows from T_flight = (E_usable / P_avg) × 60, where E_usable = C_Ah × V × eta and P_avg scales with throttle as P_hover × (throttle / 0.5)^1.5.

Why does altitude reduce flight time?

Air density falls with altitude following the International Standard Atmosphere (ISA) lapse rate. Thinner air generates less lift per RPM, so rotors must spin faster to produce the same thrust, consuming more power. At 3000 m ASL, air density is roughly 15% lower than sea level, which increases hover power and shortens flight time noticeably. High-altitude drone operations often need larger props or more powerful motors to compensate.

What is "discharge efficiency" and why 80%?

LiPo and Li-ion batteries should never be discharged to zero voltage — doing so permanently damages cells and creates a fire risk. A discharge efficiency of 0.80 means you use only 80% of rated capacity, keeping a 20% reserve. This also absorbs motor-controller (ESC) thermal losses of roughly 3–5%. Racing pilots sometimes push to 0.85–0.90, but 0.80 is the safe default for field use.

What does "figure of merit" mean for drone props?

Figure of merit (FM) compares a real rotor to a theoretically perfect actuator disk. A perfect disk has FM = 1.0; real props range from about 0.60 (cheap, small props) to 0.82 (high-quality, large props with good blade geometry). The calculator estimates FM from your thrust-to-weight ratio: high-TWR racing setups run props at high pitch angles that reduce efficiency, while lower-TWR long-endurance designs use larger, slower props with higher FM.

How does rotor diameter affect flight time?

Larger rotors have greater disk area, which means they move a larger mass of air per second to generate the same thrust. From momentum theory, power is proportional to the square root of disk loading (thrust per area), so doubling disk area at constant thrust reduces ideal hover power by about 30%. This is why long-endurance drones (survey UAVs, delivery platforms) use large, slow-spinning propellers rather than the small fast ones favoured by racing quads.

My real flight time is shorter than the calculator shows — why?

Several factors reduce real-world endurance below the physics estimate: wind requires constant corrective thrust; aggressive manoeuvres spike current draw; battery internal resistance increases at cold temperatures and causes voltage sag; video transmitters, gimbals, sensors and lights add parasitic loads; and the ESC and motor windings generate heat that represents wasted energy. For best accuracy, log your actual average current draw from a flight controller telemetry file and back-calculate to calibrate the throttle percentage input.

Drone Flight Time Calculator

Knowing how long your drone will fly before landing — or before the battery is damaged by over-discharge — is critical whether you are planning a survey grid, a cinematic orbit, or just an afternoon freestyle session. This calculator uses actuator-disk theory, the same aerodynamic framework behind helicopter and wind-turbine design, to give you a physics-grounded estimate rather than a rough rule of thumb.

How it works

Every multirotor hovers by pushing air downward. The power needed to do that is governed by the actuator-disk (momentum) model, derived from conservation of momentum and energy in the air column beneath each rotor:

P_ideal = sqrt( T³ / (2 · ρ · A_total) )

where T is hover thrust (equal to the drone’s all-up weight in newtons), ρ is air density at flight altitude, and A_total is the combined disk area of all rotors. Real propellers are not perfect actuator disks, so actual hover power is higher by a factor called the figure of merit (FM):

P_hover = P_ideal / FM

FM typically runs 0.65–0.82 for hobby props, depending on blade profile and pitch. The calculator estimates FM from your thrust-to-weight ratio.

Air density is computed from the ISA (International Standard Atmosphere) troposphere formula, which accounts for the temperature lapse rate of 6.5 K per 1000 m. This matters: at 2000 m above sea level, air density is roughly 10% lower than at sea level, requiring proportionally higher RPM and power for the same thrust.

Flight time combines that hover power with your battery energy:

T_flight (min) = ( C_mAh × V × η / 1000 ) / P_avg × 60

where C_mAh is battery capacity, V is nominal pack voltage, η is discharge efficiency (usable fraction), and P_avg is average power during the flight. Because power scales as thrust to the power of 1.5 (from momentum theory), average power at a given throttle percentage is:

P_avg = P_hover × (throttle% / 50%)^1.5

This correctly predicts the super-linear power spike when you push a drone to full throttle.

Worked example — DJI-class 1.5 kg quad

A consumer-grade quadcopter with these specs:

Parameter	Value
Battery	5000 mAh, 22.2 V (6S LiPo)
All-up mass	1500 g
Rotors	4 × 22.86 cm (9-inch)
Altitude	sea level
Discharge efficiency	80%
Average throttle	50% (calm hover)

Step-by-step:

Disk area: 4 × π × (0.1143 m)² = 0.1642 m²
Hover thrust: 1.5 kg × 9.807 = 14.71 N
P_ideal = sqrt(14.71³ / (2 × 1.225 × 0.1642)) = 89.0 W
FM ≈ 0.82 (TWR = 2, long-endurance props) → P_hover = 89.0 / 0.82 = 108.5 W
Battery energy: (5000 / 1000) × 22.2 = 111 Wh; usable: 111 × 0.80 = 88.8 Wh
P_avg at 50% throttle = P_hover × 1.0 = 108.5 W
T_flight = (88.8 / 108.5) × 60 ≈ 49 minutes

That is consistent with physics-based estimates for similarly spec’d long-range platforms. Add wind (raise throttle to 65%) and estimated time drops to around 33 minutes — consistent with real-world pilot reports for moderate-wind conditions.

Key variables and their impact

Variable	Effect on flight time
Battery capacity (mAh)	Linear — double the mAh, double the time
Rotor diameter	Strong positive — larger disk = lower power
All-up mass	Strong negative — heavier = more thrust needed
Altitude	Negative — thinner air forces higher RPM
Average throttle	Highly non-linear via the 1.5 power law
Discharge efficiency	Linear — 85% vs 75% is a 13% swing

The solve-for feature inverts the flight-time equation to tell you exactly how many mAh you need to hit a target duration — useful when sizing a battery for a specific mission before you buy.