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Skylight Rough Opening Calculator

Calculate the framed rough opening dimensions for a skylight from the unit size and manufacturer clearance.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax
1.97 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Rough opening width

2.05 ft

High confidence
Rough opening height
3.04 ft

At the values currently entered, the rough opening width works out to 0.63 m. The largest intermediate quantity is rough opening height, at 0.93 m — check that step first if the total looks off. Figures are shown for United States, where IRC 2024 is the governing residential reference; switch the market above if you are building elsewhere.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Rough opening dimension = skylight unit dimension + 2 x manufacturer-specified installation clearance (commonly 0.5in / 13mm per side)

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

Why is the rough opening larger than the skylight unit?
Manufacturers require clearance around the unit on every side (commonly 0.5in / 13mm) so the frame can be shimmed square, plumb, and level during installation without binding against the framing.
Should I use the same clearance for width and height?
This calculator applies the same clearance value to both dimensions, which matches most manufacturers' installation instructions — but always check your specific unit's spec sheet in case it calls for different clearances per side.
Does this account for curb-mounted skylights?
No — this calculates the rough opening for the skylight unit itself. A curb-mounted skylight also needs a separate curb sized per the manufacturer's curb detail, which is not covered here.