On his website, trucking safety expert witness Lew Grill, the SAGE Corporation, offers a calculator for wind chill:
WIND CHILL: A measure of the cooling effect of wind. Wind increases the rate at which a body loses heat, so the air on a windy day feels cooler than the temperature indicated by a thermometer. This heat loss can be calculated for various combinations of wind speed and air temperature and then converted to a wind chill equivalent temperature (or wind chill factor).