The prediction of a wildfire rate of spread and growth under high wind speeds and dry fuel moisture conditions is key to taking proactive actions to warn and protect communities. We investigated the possibility that a simple relationship exists that could be used as a first approximation for quickly estimating a wildfire’s spread rate simply from the open wind speed alone. We analysed data from a number of high-intensity wildfire observations (n = 118) documented in temperate shrublands, Australian dry eucalypt forests, and North American conifer forests to examine the suitability and soundness of a relationship between wind speed and rate of fire spread. The resulting rule of thumb is that the forward rate of spread of wildfires burning in forests and shrublands in relatively dry conditions is approximately equal to 10% of the average 10-m open wind speed, where both values are expressed in the same units. The rule of thumb was found to give the most accurate results for dry fuel and high wind speed conditions with reduced bias and mean relative errors lower than 50%. We further evaluated the rule of thumb against two independent databases of wildfires spreading under critical fire weather conditions. Under these conditions, the error statistics are comparable to those obtained by fire spread rate models. Best results were obtained for fires spreading faster than 2 km/h, where mean absolute percent errors were close to 20%. The rule is not applicable to grasslands.