Weather & Flight
Propeller & Drone Icing Calculator
Assess atmospheric icing hazard, dew point spread, and propeller thrust loss percentage.
Planning aid only — not certified flight-planning software or airspace clearance. Always verify results against your own aircraft's manual and check current regulations before flying. Full disclaimer.
Weather & flight parameters
Icing assessment
Severe riskSevere icing risk. The air is near freezing and close to saturation: the conditions in which propellers ice fastest. Fog, mist, drizzle or cloud can coat the propellers within minutes.
How much thrust ice costs depends on droplet size and the amount of water in the air, which this calculator can’t know. In wind-tunnel tests on a drone propeller, thrust fell by about 25% within one minute with small droplets, and almost all thrust was lost with larger ones. Read more about propeller icing.
What to do
- Don’t fly in any fog, mist, drizzle or cloud. Wind-tunnel tests have measured large propeller thrust losses within one minute of icing.
- Check propellers, arms and the camera for frost or ice before powering on.
- If already airborne, descend to warmer air and land as soon as it is safe.
What the calculator needs
- Surface temperature and relative humidity: type them in, or load them from the current forecast for a location.
- Flight height above ground: the highest point of your planned flight.
From these it estimates the temperature at your flight height, the dew point and the spread between them, and the height at which the air reaches 0°C. It then rates the icing risk.
How the risk is rated
Ice forms on propellers when they meet liquid water that is colder than 0°C. The calculator looks for that combination: air at or near freezing, and air that is close to saturation. It uses the temperature at your flight height, not at the ground.
| Risk | When it is shown |
|---|---|
| None | Above +4°C at your height, or dry air (humidity under 55% and a dew point spread over 5°C) |
| Severe | Between −4°C and +2°C with humidity of 85% or more, or a spread of 2°C or less |
| Moderate | Between −12°C and −4°C with humidity of 75% or more, or a spread of 3°C or less |
| Light | At or below 0°C with humidity of 60% or more, or a spread of 4°C or less. Also shown just above freezing, and in very cold air, which rarely holds much water but is hard on batteries |
The most severe band sits just below freezing on purpose. Near 0°C, supercooled droplets don't freeze on impact; they spread over the blade and form dense, smooth ice that changes its shape. Wind-tunnel research on drone propellers found the worst performance losses at −5°C, lessening as the air got colder. Our guide to propeller icing covers the research and what it means in practice.
Reading the outputs
Temperature at your height. The calculator lowers the surface temperature by 6.5°C per 1,000 m, the average rate at which air cools with height. At drone heights this is a small correction, about 0.8°C at 120 m. On calm, clear mornings the real air above you can be warmer than at the ground (an inversion), and in showery weather it can cool faster. Treat the figure as an estimate.
Dew point spread. The difference between the temperature and the dew point. The smaller it is, the closer the air is to forming fog, mist or cloud. A spread of 2°C or less near freezing is the strongest warning sign on the page.
Freezing level. The estimated height at which the temperature reaches 0°C, using the same average rate of cooling. If it is only a few hundred metres above you and there is low cloud, climbing is where the risk begins.
What the calculator can't see
- Visible moisture. Relative humidity measured near the ground doesn't tell you whether you'll fly through fog or cloud. If you can see mist, fog or low cloud at your flying height, assume icing is possible whenever the temperature there is at or below freezing, whatever the numbers say.
- Droplet size and water content. These decide how fast ice builds up, and they can't be worked out from temperature and humidity. That is why the calculator gives a risk level, not a predicted loss of thrust.
- Frost on the ground. A drone left in a cold car or outside overnight can have frost on its propellers before it takes off. Check before every winter flight.
Using the result
- Severe: don't fly in or near any visible moisture. If you are already airborne and notice vibration, more motor noise or the drone struggling to hold height, land straight away.
- Moderate or light: you can often fly in clear air, but stay out of fog and cloud, keep flights short, and inspect the propellers after each landing.
- Any risk level in winter: batteries lose performance in the cold, whatever the icing risk. See how cold weather affects drone batteries.
For the day's overall picture, including wind, precipitation and visibility, use Flight Window.