Fire Glass Calculator
How many pounds of fire glass a round or rectangular fire pit or fireplace takes for the depth you want, and how many bags to buy.
Result
Buy 5 bagsEstimate
Rounded up to whole bagsNo extra is added by default. Chunkier glass packs looser than fine glass, so a bag may fill more or less than this.
- Fire glass to buy
- 48 lb (21.8 kg)Estimate
- Fire glass in the pit
- 48 lb (21.8 kg)Estimate
- Volume of the layer
- 0.5 ft³ (864 in³)
https://calcgallery.com/landscaping/fire-glass-calculator/
Results are estimates for planning only. Actual needs vary with site conditions, products and workmanship. Always confirm quantities with your supplier and follow local building codes and manufacturer instructions. Read the full disclaimer
How to use the Fire Glass Calculator
- Choose a round or a rectangular fire pit and enter its inside size.
- Enter how deep the layer of glass will be, above any sand or filler underneath.
- Enter the weight of one bag or jar.
- Read the pounds of glass and the number of bags to buy.
How it is calculated
layer = length × width × depth (square or rectangular) = π × (diameter ÷ 2)² × depth (round)weight = layer × bulk densitybags = ⌈weight × (1 + allowance) ÷ bag weight⌉The bulk density comes from American Fire Glass’s use and care sheet, which says a 10 lb bag covers about a square foot 1 1/4 inches deep. That is 10 pounds in 180 cubic inches, or 96 pounds per cubic foot. The same sheet’s quick rule, height × depth × length ÷ 19, works out to about 91 pounds per cubic foot; the page uses the coverage statement, the higher of the two, so the estimate does not fall short.
Measuring the pit
Measure inside the walls, where the glass will sit, and only the depth of the glass itself. If a burner pan or a bed of sand or lava rock fills the bottom, measure from its top. A burner ring inside a round pit takes up little room and is usually ignored.
With your numbers
- Layer = plan area × 2 in = 1.178 ft³
- Glass = 1.178 ft³ × bulk density = 113.1 lb
- Bags = ⌈113.1 lb ÷ 10 lb⌉ = 12
Quick reference
No extra is added by default. Chunkier glass packs looser than fine glass, so a bag may fill more or less than this.
| Job | Bags to buy |
|---|---|
| 36 in round, 2 in deep | 12 |
| 42 in round, 3 in deep | 24 |
| 36 × 12 in, 2 in deep | 5 |
| 48 × 12 in, 3 in deep | 10 |
| 24 × 24 in, 2 in deep | 7 |
| 90 × 30 cm, 5 cm deep | 5 |
| 80 cm round, 6 cm deep | 10 |
Where the numbers come from
The fixed figures this calculator relies on, and the published source each one was checked against. How the calculators are built and checked
1 source
American Fire Glass, Fire Glass Use and Care Instructions, AFG-INST-001 Rev B 12/18, Coverage: "10-pound bag covers approximately 1 square ft x 1.25" deep". The same sheet's rule of thumb, height × depth × length ÷ 19, implies 90.9 lb/ft³; the coverage statement is used. https://americanfireproducts.com/media/manual/Fire%20Glass.pdf
Used for
- Poured bulk density of fire glass: 10 lb fills 1 ft² to 1.25 in, 96 lb/ft³. Different sizes and shapes of glass pack differently.
Common questions about the Fire Glass Calculator
- How many bags of fire glass do I need for a 36 inch fire pit?
- A round pit 36 inches across holds about 2,036 cubic inches of glass 2 inches deep. At American Fire Glass’s figure of a 10 lb bag to a square foot 1 1/4 inches deep, that is about 113 pounds, so twelve 10 lb bags.
- Why is this less than some fire glass charts?
- Some rules of thumb square the diameter of a round pit, which treats it as the square box around it and adds about 27%. American Fire Glass’s own sheet does this and divides by 19. This page works out the true area of the circle and uses the coverage the same sheet states.
- How deep should fire glass be?
- Deep enough to hide the burner, and no deeper than the burner or fire pit maker allows. Gas needs to reach the surface evenly, so the right depth over a burner is set by its instructions, not by this page. Glass away from the burner can sit on a bed of sand or lava rock to save on glass.
- Does the size of the glass change the amount?
- A little. Different sizes and shapes of glass pack with different gaps between the pieces, so a bag of large chunks may cover a different area from a bag of fine glass. If the maker of your glass gives its own coverage, change the bulk density under More options.