Calculating the number of Soapstone Firebricks needed

The first question to answer: is this for a wood-burning or gas fireplace, and what is the building code for your area?

2 ½” is the recommended soapstone firebrick thickness for lining wood-burning fireplaces.  Decorative fireplaces and gas fireplaces may call for 1 ¼” firebrick wall thickness, but be sure to check that meets your local fire code.

You are usually required to have a minimum number of inches of masonry between the flames and any combustible materials like wooden studs.  The thickness of the soapstone can usually be counted towards that masonry requirement, but make sure your building/fire inspector agrees.

Pre-manufactured modular fireplace kits like Isokern™ or Firerock™ have their own recommendations as to what thickness firebrick you can use with their models.

Soapstone is better than any other natural stone with heat, but bricks can occasionally crack, and a thicker brick will resist cracking better than a thin one.  Plus, a thicker wall gives more soapstone mass to absorb and radiate heat.

The next step is to decide what layout you want. Do you want to show the large rectangular faces of the bricks, so you have the fewest visible joints?  Or do you want narrow strips of stone laid up in a delicate herringbone pattern?  Or something in-between?  It’s also quite common for masons to use one pattern on the walls of the firebox and a different pattern on the firebox floor.

Our soapstone bricks are honed on two faces, one large and one small, which gives the mason the flexibility to lay each of them in several different configurations.  For example, our Standard bricks (9″ x 4 ½” x 2 ½”) can be installed showing the 9″ x 4 ½” face, which results in a soapstone wall thickness of 2 ½”.   Or you could lay the same bricks showing the 9″ x 2 ½” face, in which case the wall thickness would be 4 ½”.

The next step is to measure the dimensions of your firebox.  Most fireboxes are made of 4 faces: Backwall, side wall, side wall and floor.   But some designs can be more complicated.  Length in inches multiplied by height in inches = area in square inches of the wall.  Divide by 144 (which is 12 x 12) to get the square feet per wall.   So if the backwall of your fireplace is 48″ wide and 36″ high, its 48 x 36 = 1728 square inches divided by 144 = 12 SF.

Say you’ve decided to show the 9 x 4 ½” face of our standard bricks.  Each brick is 9 x 4.5 = 40.5 square inches.  Divide that by 144 and you learn that each brick covers 0.28 SF.

Take the area you intend to cover, in this example 12 SF, and divide it by the area of each brick, so 12 divided by 0.28 = 42.85 bricks.  So to cover the back wall of your fireplace you’d need 43 bricks.

If you were intending to show the 9 x 2 ½” face, then each brick only covers 0.15 SF, so for the same backwall you’d need 12 divided by 0.15 = 80 bricks.

Remember to always order extra bricks for cutting waste, especially in complicated layouts like Herringbone. The amount varies, but we typically
suggest 10%.

In the example above we have not made any allowance for the area of the joints. Our soapstone bricks are diamond sawn to be dimensionally very accurate. So you can make tight joints, like 3/16″, and therefore the area of the joints is negligible in many layouts.  In a herringbone layout, which has a lot of joints, you might want to figure something for their area.

To conclude, take the number of bricks for your back wall, side walls, and floor, add 10%, and you have your total required.  Round up to our nearest full case (25 bricks per case for Standards, 50 bricks per case for Splits, Soaps and Strips) and that’s the quantity you should order from us.

If you’d like our layout guide with images of different layouts, or our Excel spreadsheet which does a lot of the math for you, or if you have any other questions, please Contact Us.