Fire glass is tempered glass tumbled into chips or beads that withstands the heat of a gas burner and reflects the flame. It is sold by the pound, typically in 10 lb bags. A typical fill depth is 2–4 inches over the burner; many people use lava rock as a filler underneath and only a top layer of glass to save money.
How to use the Fire Glass Calculator
- Glass type
- Custom density
- Fire pit shape
- Length / side / diameter
- Width (or height of triangle / trapezoid)
- Second parallel side (trapezoid)
- Depth of glass
- Bag size
- Price per bag
- Every result field is editable: type into Weight of fire glass and Depth of glass plus every other field update to match.
Results update as you type, and every field accepts the units shown in its menu.
How it works
Choose the fire pit shape and the type of glass, enter the inside dimensions of the pit and the depth of glass. The calculator multiplies area by depth for the volume and by the bulk density of the glass for the weight, then divides by the bag size.
Tips for an accurate estimate
- Sketch the job and split irregular areas into rectangles, circles and triangles before you measure.
- Add a waste allowance – typically 5–10% for simple layouts and 15–20% for diagonal, curved or heavily cut work.
- Check the coverage or yield printed on the product, because sizes and densities vary between manufacturers.
- Buy all units of a finished material (tile, brick, siding) from the same batch so colours match, and keep a few spares for repairs.
- Confirm local prices – quarry, lumber and steel prices vary widely by region and season.
Common mistakes to avoid
- Ordering exactly the calculated amount with no allowance for breakage, offcuts and settlement.
- Forgetting to subtract doors, windows and other openings – or subtracting small ones that still need cutting around.
- Confusing US short tons (2,000 lb) with metric tonnes (1,000 kg) when comparing quotes.
Inputs explained
| Field | What to enter |
|---|---|
| Glass type | Choose one: Recycled fire glass, Reflective fire glass, Fire glass beads, Fire glass diamonds / cubes … |
| Custom density | Units: kg/m³, lb/ft³, g/cm³, lb/yd³ |
| Fire pit shape | Choose one: Rectangular, Square, Triangular, Round … |
| Length / side / diameter | Units: in, cm, mm, ft, m |
| Width (or height of triangle / trapezoid) | Units: in, cm, mm, ft, m |
| Second parallel side (trapezoid) | Units: in, cm, mm, ft, m |
| Depth of glass | Units: in, cm, mm, ft, m |
| Bag size | Choose one: 10 lb, 5 lb, 20 lb, 25 lb … |
| Price per bag | Units: /piece |
What each result means
- Volume of glass = [Area]×[Depth of glass]
- Bags = ceil([Weight of fire glass]÷[Bag size])
- Cost = [Bags]×[Price per bag]
Example values
How the main result changes when Depth of glass changes and everything else stays at the example values above:
| Depth of glass (in) | Weight of fire glass (lb) |
|---|---|
| 1 | 45.1 |
| 1.5 | 67.7 |
| 2 | 90.2 |
| 2.5 | 112.8 |
| 3 | 135.3 |
| 4 | 180.4 |
Formula
Volume = area × depthWeight = volume × density (≈ 1.44 g/cm³ for recycled fire glass)Bags = weight ÷ bag weightWorked example
Inputs — Glass type: Recycled fire glass; Custom density: 1,440 kg/m³; Fire pit shape: Rectangular; Length / side / diameter: 36 in; Width (or height of triangle / trapezoid): 24 in; Second parallel side (trapezoid): 18 in; Depth of glass: 2 in; Bag size: 10 lb; Price per bag: $40 /piece.
Results — Area = 864 in²; Volume of glass = 1,728 in³; Weight of fire glass = 90.2 lb; Bags = 10; Cost = $400.00.
Frequently asked questions
How much fire glass do I need?
Multiply the pit's area by the depth for the volume, then by about 1.44 g/cm³ (≈ 0.052 lb/in³). A 36 in round pit filled 2 in deep needs about 105 lb.
How deep should fire glass be?
At least 1–2 in above the burner; 2–4 in in total is typical.
Can I put lava rock under fire glass?
Yes – a lava rock base with a 1–2 in layer of glass on top cuts the cost considerably.
Does fire glass burn?
No. Tempered fire glass does not burn, melt or produce smoke or soot at fire pit temperatures.
What formula does the Fire Glass Calculator use?
Volume = area × depth.