How to Figure the Brick Lintels for Windows

Measure the rough opening of the window with a tape measure before you start laying brick, and calculate the number of brick courses that will go on top of the window as a guide to how much weight the lintel will have to support. Consult with a lintel supplier about the gauge or thickness of steel needed to hold that weight. Most house lintels will be 1/4 to 3/8 inch thick, which will conform to brick mortar joints.

Add at least 4 to 8 inches on each side to the width of the rough window opening as a basic calculation; that would be from half a brick to a full brick on either side. Figure a lintel for a rough opening of 32 inches to be 40 to 48 inches wide, for instance, depending on the number of bricks it must hold. Use 4 inches as a minimum for a window whose top opening is at or near the top of the wall.

Use a triangular scheme to calculate lintels more exactly. Make a triangle whose peak is half the width of the rough opening. Figure that a 40-inch lintel above a 32-inch window, for instance, would have a triangle peak of 20 inches and so should support about five courses of brick. Adjust the width to conform to the number of courses of brick to go above the window.

Install lintels on top of the rough opening and extending into mortar joints on each side. Measure the distance to the top of the window when bricks are about halfway up the sides and adjust mortar joints if needed so the top of a brick course will be even with the rough opening to allow the lintel to fit neatly into the mortar joint.