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How to Measure a Fireplace for Gas Logs — 4 Numbers, 3 Minutes

Gas Logs · Measuring Guide

Measuring your fireplace is the most important step when shopping for gas logs. Four numbers — front width, rear width, height and depth — determine the largest set that fits safely. Three minutes with a tape measure is all it takes.

Open the Sizing Tool Call (949) 619-7824

Enter your four numbers in the tool and it recommends the right log set size automatically

The Four Numbers

What to measure — and where

Most fireboxes taper: the back wall is narrower than the front opening. That's why gas logs need both widths, plus height and depth. Here is every measurement on one diagram:

Firebox measuring diagram Cutaway view of a fireplace firebox showing four measurements: A rear width across the back wall, B depth from the front opening to the back wall, C front width across the opening, and D height from the floor to the top of the opening. BACK WALL A · Rear width B · Depth C · Front width D · Height
A Rear width — across the back wall B Depth — front opening to back wall C Front width — across the opening D Height — floor to top of opening
Step by Step

Three minutes, a tape measure, done

C
Front width — the opening
Measure straight across the front opening of the fireplace, side to side at the face.
A
Rear width — the back wall
Reach in and measure the width of the rear fireplace wall. On tapered fireboxes this is the smaller number — and it limits your log set length.
D
Height — floor to top
Measure from the firebox floor to the top of the front opening.
B
Depth — front to back
Measure from the front opening to the rear wall along the firebox floor.

Write all four down. The size of your fireplace and the size of your gas logs' fuel control system together determine which sets fit — the sizing tool applies the exact rules for you.

Fit Rules

The four rules that decide your size

1
Keep 2″ clear on each side
A minimum of 2 inches on both sides must be maintained between the burner system and the fireplace sidewalls — many customers prefer up to 6 inches for a more open look.
2
Rear wall sets the limit
The log set should not be longer than the width of the rear fireplace wall — that's why rear width matters as much as front width.
3
Depth: 12–14″ minimum
Almost all gas log sets need a firebox at least 12 to 14 inches deep.
4
Leave room for the controls
The burner's fuel control system (valve, pilot) needs space too — factor it in when comparing set dimensions to your firebox.
Quick Reference

What size set fits your firebox

Firebox front width Typical log set size
24–30″ wide 18″ log set
30–36″ wide 24″ log set
36–48″ wide 30″ log set

Guideline only — exact fit depends on rear width, depth and the burner system. The sizing tool checks all of it.

Sets across the size range

18″ set Real Fyre 18 inch American Oak vented gas log set
American Oak 18″
Real Fyre · for fireboxes 24–30″ wide
View set
24″ set Real Fyre 24 inch Split Oak Designer Plus vented gas log set
Split Oak Designer Plus 24″
Real Fyre · for fireboxes 30–36″ wide
View set
30″ set Real Fyre 30 inch Rustic Oak vented gas log set
Rustic Oak 30″
Real Fyre · for fireboxes 36–48″ wide
View set

Browse the full range in the gas logs collection, or read the Gas Logs Buyer's Guide for fuel types, vent types, ignition systems and brands.

FAQ

Measuring questions we hear most

My back wall is narrower than the front. Which width do I use?
Use both. The front width points you at the typical set size, but the log set should not be longer than the rear wall width — on tapered fireboxes the rear wall is the real limit.
How much side clearance do gas logs need?
Keep a minimum of 2 inches on both sides between the burner system and the fireplace sidewalls. Many customers prefer up to 6 inches per side for a more open, balanced look.
My firebox is shallow. Will gas logs fit?
Almost all gas log sets need a firebox at least 12 to 14 inches deep. If yours is shallower, call us at (949) 619-7824 — a fireplace specialist will check slim-profile options against your exact dimensions.
Free Expert Help

Rather measure with a pro on the line?

Our Fireplace Professionals will walk you through every number by phone and make sure the set you order is the perfect fit for your fireplace — before you pay a cent.

Call (949) 619-7824 Use the Sizing Tool

Or browse all gas log sets once you have your four numbers.