Wind Gust Factor Calculator
The wind gust factor is the ratio of peak gust wind speed to mean sustained wind speed. It quantifies the gustiness of the wind and is an important parameter in aviation, fire weather, structural engineering, and outdoor safety planning. A gust factor of 1.0 means perfectly steady wind; values above 1.3 indicate significant turbulence. Convective storms, frontal passages, and complex terrain all produce high gust factors. Enter the gust speed and sustained wind speed to compute the gust factor, or enter sustained wind and a desired gust factor to estimate the expected gust.
Gust factor formula
Gust Factor = Peak Gust Speed / Sustained Wind Speed
Estimated Gust = Sustained Wind * Gust Factor
The gust factor is dimensionless. If you provide both sustained and gust speeds, the calculator computes the observed gust factor. If you provide a gust factor and sustained speed without a measured gust, the calculator estimates the expected gust speed.
Gust factor reference values by environment
- Open flat terrain (stable): 1.2-1.4.
- Suburban or wooded terrain: 1.4-1.6.
- Convective outflow or squall lines: 1.5-2.5.
- Severe thunderstorm: 2.0-3.0 or higher.
- Complex or mountainous terrain: 1.5-2.0 depending on flow alignment.
Wind gust factor: frequently asked questions
What is the wind gust factor?
The gust factor (GF) is the ratio of the peak wind gust to the mean (sustained) wind speed over a standard averaging period, typically 10 minutes for WMO standards or 2 minutes for US aviation (ASOS). Gust factors greater than 1.3 are operationally significant. Values of 1.5-2.0 are common in convective environments.
What gust factors are typical for different weather conditions?
Open terrain steady wind: gust factor approximately 1.2-1.4. Convective or thunderstorm outflows: 1.5-2.5. Frontal passages: 1.3-1.8. Complex terrain or forest: 1.4-2.0. Coastal sea breeze: 1.1-1.3. Higher instability and greater turbulence generally produce higher gust factors.
How are gusts and sustained winds defined by NWS?
The NWS defines sustained wind as the average speed over a 2-minute period. A gust is the maximum instantaneous wind speed recorded during a 2-minute observation period. Gusts are reported when the peak speed exceeds the average speed by 10 knots or more (or 15% per some sources).
Why do gust factors matter for fire weather?
High gust factors combined with low humidity and dry fuels create extreme fire behavior. Sudden gusts can cause rapid fire spread, blow spotting embers far ahead of the fire line, and overwhelm firefighting resources. The NWS issues Red Flag Warnings when critical fire weather conditions including high gusts are forecast.
Can I estimate what gust speed to expect from sustained wind?
Yes. If you know a typical gust factor for the weather pattern and terrain, multiply the sustained wind by the gust factor. For example, a 20 mph sustained wind with a gust factor of 1.5 suggests expected gusts of 30 mph. This is a probabilistic estimate; actual gusts depend on atmospheric stability, terrain, and storm characteristics.
Official sources
- NOAA/NWS: NWS Wind Terminology.
- WMO Guide to Meteorological Instruments: WMO CIMO Guide: Wind Measurement.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.