Determine the Size of Hinge

Determine the Size of Hinge 

Height of Hinge

The first thing to find is the height of the hinge. Follow the examples below. These are only examples. Job situations will offer many more variables. Only on the full mortise hinges are there two dimensions, such as a 4-1/2” x 4-1/2” (114 x 114 mm). The first dimension indicates the height and the second dimension indicates the width when the hinge is in the open position.

Width of Hinge 

There are three dimensions to know in order to determine the minimum width of the hinge: door thickness, hinge backset, and clearance required. 

1. When figuring the calculations for a wood door and wood frame, the door is flush with the casing or face of the frame. When figuring the calculations for a wood or metal door with a hollow metal frame, the door is inset approximately 1/8” (3.2 mm). 

2. For doors up to 2-1/4” (57 mm) thick, the hinge backset is 1/4” (6.4 mm) from the back face of the door. 

3. For doors over 2-1/4” (57 mm) thick, the hinge backset is 3/8” (9.5 mm) from the back face of the door. 

Once these dimensions are known, the formula can then be applied. Take the door thickness, subtract the backset, multiply by two, and add the clearance required. If the hinge size is not standard, then go to the next larger hinge width. If the width of the hinge is greater than the height of the hinge [example: 4-1/2” x 6” (114 mm x 152 mm)] this is referred to as a wide throw hinge. This would apply only to full mortise hinges.

Determine the Number of Hinges

The next determination is the number of hinges per door leaf. A general rule of thumb: one hinge for every 30” (762 mm) of door height or fraction thereof. 

Door Height                                             Number of Hinges

Up to 60” (1524 mm)                                           2 Hinges 

Over 60” (1524 mm) and not over 

90” (2286 mm)                                                     3 Hinges

Over 90” (2286 mm) and not over 

120” (3048 mm)                                                   4 Hinges 

For doors with a width greater than 37” (940 mm) to 48” (122 mm), an extra hinge could be used for additional strength. The extra hinge helps support the additional weight and tension applied to the frame created by the wider door width.

Doors up to 60” (1524 mm) in height shall be provided with two hinges and an additional hinge for each additional 30” (762 mm). Where spring hinges are used, at least two shall be provided