Measure the length of the doorframe, including screen doors and frames.
Measure the number of inches from the concrete or ground to the bottom of the door frame.
Measure the length of the doormat you want, including trim and borders. Choose a doormat that runs the length of the doorframe; the diameter of oval and circular doormats should equal the length of the doorframe. The far left and far right edges should meet the far left and far right edges of the frame.
Measure the thickness of the doormat you want. Wicker and rubber doormats can measure several centimeters high. Choose a doormat with a thickness shorter than the space between the bottom edge of the doorframe and the concrete or ground.
Open the door several times to make sure the doormat is not pulled when the door is open and closed.