How to Measure Glass for a Window

Start by removing the existing glass from the window. Wear leather work gloves to protect your hands and safety goggles to protect your eyes. Apply masking tape in a crisscross pattern across the glass on the inside and outside of the window. This will help to keep the glass from shattering into too many pieces. Cover the glass with sheets of newspaper, taping them securely on to the window and sash. When you break the glass the newspaper will catch any of the small shatter pieces created.

Tap the glass firmly with your rubber hammer until it breaks. The tape will hold most of the glass together. Carefully remove the newspaper and fold it around the loose pieces. Remove the larger pieces that remain lodged in the frame. Work the remaining smaller pieces back and forth with your hands until they are loose enough to remove. Use the hammer to knock out any stubborn pieces. You may need to pry some of the pieces out with a putty knife.

Use a putty knife to remove any old glazing or putty. For an accurate measurement it will be important to have a nice clean window frame. Old glazing is easier to remove when heated. A heating gun will help with this step.

Take two inside edge width measurements, one at the top and one at the bottom of the window frame. Take two inside edge length measurements, one at the left side and one at the right side of the window frame.

Draw a rough sketch of the window shape on a piece of paper and write down the smallest width and smallest length measurements. Subtract 1/8 inch from each measurement. This will allow for any expansion and contraction of the window frame. Take this information to your local hardware store and have the glass cut to size.