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From the edge of the opening to the nearest edge of the mantel or trim.
Measure from the opening itself — the top of the firebox opening for a mantel shelf, the side of the opening for side trim — to the closest point of the combustible piece.
How far the combustible piece stands out from the masonry face.
The depth of the mantel shelf or the thickness of the trim, measured out from the fireplace front it is fixed to.
Least distance from the opening
12 in
At the distance entered the projection may be at most 1.25 in, so the piece entered does not fit there.
- Greatest projection at the distance entered
- 1.25 in
- Nearest any combustible may come
- 6 in
- Distance beyond which projection is not limited
- 12 in
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Fireplace Mantel Clearance Calculator: 12 in — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- International Code Council, 2021 International Residential Code, R1001.11 exception 4: combustible mantels or trim not within 6 in (152 mm) of a fireplace opening; within 12 in (306 mm) of the opening, a projection of no more than 1/8 in (3 mm) for each 1 in (25 mm) of distance from it
Inputs used
- Distance from the fireplace opening
- 10 in
- Mantel or trim projection
- 1.5 in
Intermediate steps
- Greatest projection at the distance entered
- 1.25 in
- Nearest any combustible may come
- 6 in
- Distance beyond which projection is not limited
- 12 in
Confidence note: At the distance entered the projection may be at most 1.25 in, so the piece entered does not fit there.
What this calculation does not cover
- This is the IRC's rule for masonry fireplaces. A factory-built fireplace, an insert or a stove follows its listing and installation instructions, which often ask for more clearance, and a jurisdiction may amend the code it adopts.
- The IRC prints its metric equivalents rounded — 6 inches as 152 mm, 12 inches as 306 mm; the page works in inches and converts exactly, so a metric figure can differ from the printed one by a millimetre or two.
- The rule covers exposed mantels and trim on the fireplace front. Wood framing behind and beside the masonry has its own clearances from the fireplace's faces, and trim at the sides is also held back from the firebox lining; neither is worked here.
Add the equipment this sizes
This result is a specification — 12 in — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-25 · v1.0.0
Regulatory standards & verification citations1
Which documents these citations point at
- International Residential Code (United States)One- and two-family dwellings and townhouses up to three storeys — structure, fire safety, energy, plumbing, mechanical and electrical in a single document.
A code or standard has force only where a jurisdiction has adopted it, usually with local amendments. This site holds no adoption data for any authority, so check what is in force with the authority where you build. Any section cited above without an edition should be checked against the edition in force where you build. What it would take to know.
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