Firebrick Calculator

Determine full and split refractory firebrick counts and high-temperature premixed mortar for fireplaces, wood stoves, and pizza ovens.

Firebox Width (in)

Firebox Depth (in)

Firebox Height (in)

Brick Size

Laying Pattern

Firebricks Required

112 Bricks

26.1 sq ft Total Interior Surface (3 walls + floor)

Refractory Mortar 2 Pails 15 lb pails (HeatStop/Rutland)

Joint Thickness 1/16" - 1/8" Tight dipped joints

Never Use Standard Portland Mortar! Standard masonry mortar breaks down and explodes at temperatures above 500°F. High-temperature refractory mortar rated to 2,500°F+ (ASTM C199) is mandatory for fire contact.

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How Firebox Brick Counts Are Calculated

A standard fireplace firebox lines 4 distinct surfaces: the floor (hearth), back wall, left side wall, and right side wall:

Surface Area = (Width × Depth) + (Width × Height) + (2 × Depth × Height)
Firebrick Area = 9" × 4.5" = 40.5 sq inches = 0.281 sq ft
Total Bricks = (Total Surface Area / 0.281) × 1.10 (10% cutting waste)

Frequently Asked Questions

What is the difference between full and split firebricks?

Full firebricks are 2-1/2 inches thick and used for firebox walls and wood ovens. Split firebricks are half as thick (1-1/4 inches) and used to line wood stove fireboxes where space is constrained.

How are firebricks mortared together?

Firebricks are laid with extremely tight joints (1/16" to 1/8"). The bricks are typically "buttered" with thin refractory mortar slurry and pressed firmly into place.

Can red clay clay bricks be used in a firebox?

Never. Standard red clay bricks contain trapped moisture and minerals that cause them to spall, crack, and potentially explode when subjected to intense direct wood fire temperatures.