Free Fire Glass Calculator Online

When designing or updating a fire pit, fireplace, or gas burner, using the correct amount of fire glass is essential for aesthetics, heat distribution, and safety. A fire glass calculator is a practical tool that gives you an accurate estimate based on the dimensions of your burner pan, firebox, or fire feature.

Using too little fire glass can expose burner parts and reduce efficiency, while using too much adds unnecessary cost. Whether you’re a homeowner, contractor, or landscape designer, this calculator ensures you get the right volume of fire glass for a clean, modern finish.

Fire Glass Calculator

What Is Fire Glass?

Fire glass is tempered, heat-resistant glass designed for use in fire features. It doesn’t burn, melt, or emit fumes. Instead, it reflects light and radiates heat, offering a modern alternative to lava rock or traditional gas logs.

Fire glass is measured in cubic inches, cubic feet, or pounds, depending on the type, size, and density of the glass. To calculate how much you need, you must first determine the volume of your burner area.

fire glass calculator

Why Use a Fire Glass Calculator?

Manual estimation can be inaccurate, especially for unique fire pit shapes. A fire glass calculator simplifies the process by:

  • Calculating exact volume based on your pit’s or tray’s shape and dimensions
  • Converting volume into cubic feet, cubic inches, and pounds
  • Saving time and reducing material waste
  • Providing fast answers for DIY and contractor-led projects

Fire Glass Calculator Formula (Rectangular Fire Pit)

For a rectangular burner area, use the following formula to calculate volume in cubic inches: $$Volume (in3)=Length (in)×Width (in)×Depth (in)\text{Volume (in}^3) = \text{Length (in)} \times \text{Width (in)} \times \text{Depth (in)}Volume (in3)=Length (in)×Width (in)×Depth (in)$$

Then convert to cubic feet: Volume (ft3)=$$Volume (in3)1728\text{Volume (ft}^3) = \frac{\text{Volume (in}^3)}{1728}Volume (ft3)=1728Volume (in3)​$$

Convert to pounds (using average fire glass density of ~7 lb/ft³): $$Weight (lb)=Volume (ft3)×7\text{Weight (lb)} = \text{Volume (ft}^3) \times 7Weight (lb)=Volume (ft3)×7$$

Example Calculation – Rectangular Fire Pit

Dimensions:

  • Length: 36 inches
  • Width: 12 inches
  • Depth: 2 inches

Step 1: $$Volume (in3)=36×12×2=864 in3\text{Volume (in}^3) = 36 \times 12 \times 2 = 864\ \text{in}^3Volume (in3)=36×12×2=864 in3$$

Step 2: $$Volume (ft3)=8641728=0.5 ft3\text{Volume (ft}^3) = \frac{864}{1728} = 0.5\ \text{ft}^3Volume (ft3)=1728864​=0.5 ft3$$

Step 3: $$Weight (lb)=0.5×7=3.5 lb\text{Weight (lb)} = 0.5 \times 7 = 3.5\ \text{lb}Weight (lb)=0.5×7=3.5 lb$$

Result: You need approximately 3.5 pounds of fire glass.

Fire Glass Calculator Formula (Circular Fire Pit)

For a round fire pit, use: $$Volume (in3)=π×(Diameter2)2×Depth\text{Volume (in}^3) = \pi \times \left( \frac{\text{Diameter}}{2} \right)^2 \times \text{Depth}Volume (in3)=π×(2Diameter​)2×Depth$$

Then convert as shown above to cubic feet and pounds.

Example – Circular Fire Pit

Dimensions:

  • Diameter: 24 inches
  • Depth: 2 inches

Step 1: $$Volume (in3)=π×(12)2×2≈3.14×144×2=904.32 in3\text{Volume (in}^3) = \pi \times (12)^2 \times 2 \approx 3.14 \times 144 \times 2 = 904.32\ \text{in}^3Volume (in3)=π×(12)2×2≈3.14×144×2=904.32 in3$$

Step 2: $$Volume (ft3)=904.321728≈0.52 ft3\text{Volume (ft}^3) = \frac{904.32}{1728} \approx 0.52\ \text{ft}^3Volume (ft3)=1728904.32​≈0.52 ft3$$

Step 3: $$Weight (lb)=0.52×7≈3.64 lb\text{Weight (lb)} = 0.52 \times 7 \approx 3.64\ \text{lb}Weight (lb)=0.52×7≈3.64 lb$$

Result: You need approximately 3.64 pounds of fire glass.

Fire Glass Depth Guidelines

Recommended fire glass depth varies by burner type:

  • 1.5 to 2 inches – Most common for tray or pan burners
  • 2 to 4 inches – For deeper fireboxes or sunken fire pits
  • Avoid deeper than 4 inches, which may affect flame height and gas flow

Shapes Supported by the Fire Glass Calculator

  • Rectangular burner pans
  • Circular pits
  • Square fire features
  • Custom shapes (estimate using subdivision or averages)

Common FAQs

Q1: How much fire glass do I need for a fire bowl?
Use the circular formula above. Measure the diameter and depth of the bowl interior.

Q2: Does fire glass settle over time?
Slightly. Refill may be needed after initial use and gas testing.

Q3: What if I have lava rock underneath?
Only calculate depth for the top visible layer of fire glass (typically 1–2 inches).

Q4: Can I reuse fire glass?
Yes. It’s heat-resistant and reusable, but make sure it’s clean and intact.

Q5: Is all fire glass the same weight?
No. Some colored glass or specialty blends may weigh more or less than 7 lb/ft³.

Pro Tips for Fire Glass Installation

  • Always use tempered fire-rated glass
  • Layer with lava rock or crushed stone for deep trays to save cost
  • Keep glass clear of burner holes to avoid clogging
  • Rinse before use to remove dust and residue
  • Never exceed manufacturer-recommended depth

Final Thoughts

A fire glass calculator eliminates the guesswork from fire feature installations. Whether you’re building a linear fire table, a circular pit, or a custom wall-mounted fireplace, getting the right volume of fire glass ensures performance, safety, and style.

Remember the key formula: $$Weight (lb)=(Length×Width×Depth1728)×7\text{Weight (lb)} = \left( \frac{\text{Length} \times \text{Width} \times \text{Depth}}{1728} \right) \times 7Weight (lb)=(1728Length×Width×Depth​)×7$$

Start your project with confidence, knowing exactly how much fire glass you need for a clean, modern finish.