News & Media

How to Measure Your Skylight

January 4, 2018 | General Info, Tech Help

Measuring a custom sized curb
Our team measures a custom shaped curb in Gig Harbor

“OD” (Outside Curb Dimensions)
This is the primary dimension that we use to ensure that our skylights are custom built to fit perfectly. When measuring the outside curb dimension, you must measure the outside edge to edge of the curb, including any existing flashing.
In terms of a shoebox, this is the outside of the shoebox’s dimensions.

“Actual” (Actual Skylight Inside Dimensions)
The “Actual” Dimension is the measurement that spans the inside of the skylight’s inner frame. Imagine flipping the skylight upside down and measuring the interior frame, edge to edge. Typically we add ¼ of an inch to each of the four sides of the skylight’s outside curb to get a skylights “Actual” dimension. For example, if the “OD” is 34”x34”, the “Actual” = OD + ¼ + ¼ = OD + ½ = 34½ x 34½.
In terms of a shoebox, this is the inside measurement of the shoebox lid.

“OFD” (Outside Existing Frame Dimensions)
The outside frame dimension is the most difficult dimension for us to use. Different manufacturers have different sized skylights, with different skylight frames. This means that the “OFD” tells us very limited information about the curb size.
In terms of the shoe box analogy, the OFD would be the outside of the shoe box lid. If you have two shoe box lids with the same outer dimensions, but one is much thicker than the other, the thicker shoe box lid will not fit as well as the thinner shoe box. The same applies to skylights! 

If you have any further questions about sizing please do not hesitate to call us at 206-763-6868 or email us at

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