To read a wind chill chart, find the current outside temperature along the top of the chart, the closest wind speed from the numbers on the left edge, and then find where these two numbers intersect on the chart. To do the latter, use your finger to follow the numbers down from your selected average temperature. Do the same with your wind speed selection, only go horizontally towards the right until you intersect the number under your selected temperature.
The point where the two lines intersect is the wind chill factor. It's easier if your use one finger on each hand to trace the lines to where they meet. Some charts, like those produced by the National Oceanic and Atmospheric Administration, or NOAA, are in color, also making them easier to use. The NOAA chart also lists the amount of time it takes to get frostbite for different temperatures. To find the frostbite information, find the wind chill factor as described above then use the color codes to find the frostbite times.
For example, if you had a temperature of minus 10 degrees Fahrenheit and a wind speed of 30 mph, you'd have a wind chill factor of minus 35 degrees Fahrenheit. That puts your wind chill in the dark blue frostbite zone. That means that unexposed skin can get frostbitten in about 10 minutes.