Where the arithmetic is, and where the honesty is
The arithmetic is one line. Usable capacity in amp-hours, divided by average current in amps, times sixty, gives minutes. A 5,200 mAh pack is 5.2 Ah; take 75 percent of it and you have 3.9 Ah; at 24 amps that is 0.1625 hours, or 9.75 minutes. Nothing about that is difficult and nothing about it is where people go wrong.
Where people go wrong is the current figure. Hover current is not cruise current, and neither is the current you draw doing actual work. A hover is the cheapest thing a multirotor does. Every input you give it costs power on top: climbing costs a lot, holding position against wind costs a lot, and a payload costs more than its weight suggests. A manufacturer's flight time is measured in the most favourable way it can honestly be measured — still air, no payload, a steady hover, and the pack taken down further than you would take it. That is a valid number and it is also a ceiling you will never see on a working flight.
Why a payload costs more than its share
A rotor does not pay for lift in proportion to the lift. From momentum theory the induced power required goes as thrust to the power of one and a half, so adding ten percent to the weight costs roughly fifteen percent more power in hover. This calculator applies that exponent to your payload. Add 300 g to a 1,400 g aircraft, an increase of about 21 percent, and it applies a factor of about 1.34 to the current.
That is an approximation and it is deliberately a coarse one. The real penalty depends on disc loading, on how far the props are from their efficient operating point once loaded, and on whether the payload also adds drag — a boxy sensor hanging in the airflow costs more than a flat plate tucked into the body. Treat the payload factor as a first estimate and replace it with a measured average current from telemetry the first time you fly the configuration for real.
Reserve is not the same thing as the usable share
The two fields do different jobs and both are needed. The usable share is a battery health decision: how much of the pack you are prepared to take out on a routine flight, given that repeatedly running a lithium pack near empty shortens its life more than any other single habit. Something in the region of 70 to 80 percent is a common working figure.
The landing reserve is an operational decision: the minutes you keep for the approach, for a go-around because someone walked into the landing area, and for the fact that the aircraft is not directly overhead when the low warning sounds. It is time, not percentage, because the risk it covers is time-shaped. Two minutes is a starting point for a small machine landing where it took off. If you are working a quarter mile out with a headwind on the way home, two minutes does not cover the return trip.
| What changed | Effect on endurance |
|---|---|
| 15 mph wind, working into it half the time | Commonly 15 to 30% shorter |
| Continuous translation rather than hover | Slightly better at moderate speed, worse at high speed |
| Cold pack, near freezing | Noticeably less usable capacity and a sagging voltage |
| Pack past its useful life | Less capacity and more sag under load, together |
| High density altitude | More power for the same lift |
Where this feeds into the rest of the planning
Endurance is only half of any survey plan. Once you know minutes per pack, the drone survey coverage calculator turns that into how many packs a site needs, and the drone mapping and GSD calculator sets the flight lines those minutes are spent on. If the payload figure above is close to the limit, work the margin properly with the drone thrust to weight calculator before you fly it, and check the pack itself against the LiPo pack and charging calculator.
The two things that actually hurt people
Lithium polymer packs are a real fire hazard, not a theoretical one. A pack that has been punctured, crushed in a crash, swollen into a pillow shape, or run flat below its cutoff can ignite without warning and burns hot enough that smothering it is not a plan. Almost every pack fire that gets written about happened while the pack was charging with nobody in the room. Charge where you can see it, on a surface that does not care, and stop the charge if a pack gets hot or gains thickness. A damaged pack should be moved away from anything that will burn and kept there; for getting rid of it, follow whatever your local hazardous waste program says, because that is a local question and not one a website should answer.
Propellers cut. They are stiff, they turn fast, and a multirotor that has armed on the ground is a running machine. A drone that loses a motor in flight does not glide anywhere; it comes down more or less where it was. Keep people out from under the aircraft and keep your hands away from the arms while the battery is connected.
What this page does not tell you
Nothing on this page is a statement of law and no number it produces is evidence of compliance. Drone flight in the United States is regulated federally, the rules for recreational flying and for flying as part of a business are not the same set of rules, and they are revised. There are requirements around who may operate, what has to be registered, what has to broadcast identification, and where you may fly at all; controlled airspace requires authorization before you enter it, obtained through the official channels. None of those are described here on purpose, because a stale summary on a calculator page is worse than no summary. Check the current requirements at the FAA and use the official airspace tools before every flight, not once when you bought the aircraft.
State, county and city rules sit on top of the federal ones and cover things federal rules do not: where you may take off and land, what happens over a park or a beach, and privacy. They vary between neighbouring towns. Find out who owns the ground you launch from and what they allow.
A planned altitude, a planned standoff or a planned flight line from this calculator is an engineering figure for a camera and a battery. Whether you may actually fly it is a separate question with a separate answer.
Questions people ask
Why is my flight time so much shorter than the advertised figure?
Because the advertised figure and your flight are not the same test. A quoted endurance is typically a still-air hover, no payload, at a sensible temperature, run until the pack is much emptier than you would choose to run it. Your flight has wind, has climbs and descents, probably has a payload, and you land with something left. Each of those is worth minutes on its own, and they stack. If you want a like-for-like comparison, set the payload to zero, the wind penalty to zero and the usable share to 100 percent in this calculator, and the still-air hover figure it produces is roughly the number a spec sheet is quoting.
Does a bigger pack always give a longer flight?
No, and this is the trap in buying up. A bigger pack adds weight, the extra weight costs power at better than a one-to-one rate, and past a certain point the added capacity is spent carrying the pack that holds it. Every airframe has a capacity where endurance peaks and then falls away. The way to find yours is empirically: fly two pack sizes you already have, record the average current and the actual minutes for each, and see which direction the curve is going. For work that needs long total time rather than long single flights, more packs and a fast swap almost always beats one huge pack.
What average current should I use if I have never measured one?
Use the estimate mode, which works from weight and a hover efficiency figure in watts per kilogram. Small aircraft with small fast propellers land around 180 to 220 W/kg; larger airframes with big slow props are better, sometimes near 100 W/kg. That range is wide because it is genuinely wide, so treat the answer as an order of magnitude rather than a plan. Then fly one flight with telemetry logging, take the average current over the whole flight rather than the peak, and put that number in. One measured flight is worth more than any estimate on this page.
Should the usable share be the same for every pack?
Not necessarily. A new, healthy pack with plenty of headroom will hold voltage under load down to a lower state of charge than a tired one, so the same percentage feels different. What matters more than the percentage is what the pack voltage is doing under load near the end of the flight: a pack that sags hard when you climb has less usable capacity than its state of charge suggests, regardless of what the percentage says. Watch voltage under load, not just the fuel gauge, and lower the usable share as a pack ages.
Does cold weather really change this much?
Yes. Lithium packs deliver less usable capacity when cold and their internal resistance rises, so the voltage sags further for the same current and the low-voltage limit arrives earlier in the flight. In genuinely cold conditions it is normal to lose a meaningful share of the endurance, and the loss is worse on an old pack than a new one. Packs that have been kept warm before the flight do better than packs taken out of a cold vehicle, which is why people carry them inside a jacket. Plan the shorter number, not the one you get in summer.