How to Size for the Drip Edge

Updated February 21, 2017

Drip edge or drip cap as it is sometimes called is designed to help direct water away from the top of windows. Common materials for drip edge include wood, vinyl and sheet metals such as aluminium. The drip edge is installed on the window during installation once the window has been flashed but before the siding is installed. The overhang on either side of the window should be at least 1/4 inch so it will help protect the window.

Measure the width of the window from the outside edges of the frame at the top end of the window using a tape measure.

Add at least 1/2 inch to the measurement from Step 1 so the drip edge will overhang on each side by at least 1/4 inch.

Lay the drip edge on a work surface. Measure the drip edge to the length you added up in Step 2. Mark the drip edge with a pencil.

Cut the drip edge at the pencil mark in a straight line using tin snips to cut it to length. Snip the metal as you would paper when using scissors.


Select a drip edge in a colour that will blend in with your window trim colour or have it painted to match.


Wear eye protection when cutting drip edge.

Things You'll Need

  • Tape measure
  • Aluminium drip edge
  • Tin snips
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About the Author

Jonah Morrissey has been writing for print and online publications since 2000. He began his career as a staff reporter/photographer for a weekly newspaper in upstate New York. Morrissey specializes in topics related to home-and-garden projects, green living and small business. He graduated from Saint Michael's College, earning a B.A. in political science with a minor in journalism and mass communications.