Forge Burner BTU & Sizing Calculator
Quick answer
Enter your forge's inner chamber dimensions and this tool returns the chamber volume, the total BTU/hr it needs to reach forging heat, and how many burners of what size to run. Rule of thumb: one 3/4 in naturally-aspirated burner (~90,000 BTU/hr) heats about 350 cubic inches; a 1 in burner about 700. Add ~25% for forge welding.
Burner & BTU
A 4.0 in dia x 9.0 in chamber is about 113 cubic inches. Rule of thumb: one 3/4 in naturally-aspirated burner heats ~350 in³, a 1 in burner ~700 in³.
| Chamber volume | Burner setup | Rough BTU/hr | Best for |
|---|---|---|---|
| Up to 350 in³ | One 3/4 in | ~90,000 | Knives, hooks, small work |
| 350-700 in³ | One 1 in, or two 3/4 in | ~150,000-170,000 | General work + light welding |
| 700-1,050 in³ | Two 3/4-1 in | ~180,000-200,000 | Longer / heavier stock |
| Over 1,050 in³ | Three+ burners | 250,000+ | Big or production forges |
How much BTU a propane forge needs
Burner size follows chamber volume, not the other way around. A naturally-aspirated 3/4 in burner puts out roughly 90,000 BTU/hr and comfortably heats about 350 cubic inches of well-insulated chamber. A 1 in burner (~150,000 BTU/hr) covers up to about 700 in³. Multiply up from there.
Two things change the math: insulation and welding. A poorly lined forge leaks heat and acts bigger than it is, so line it properly first - our forge insulation calculator tells you how much kaowool and rigidizer you need. And forge welding wants roughly 25% more heat than plain forging, which is why welders reach for a 1 in burner and a 0-30 PSI regulator.
Bigger is not better
Oversizing a burner wastes propane and overheats a small chamber, scaling and even melting your stock. Size to the chamber, insulate well, and use a regulator you can turn down. Once you know your BTU, drop it into the propane forge cost calculator to see what an hour of forging will actually cost, and the propane tank size guide to make sure your tank can keep up.
Burners and gas train for this size
A burner sized to your chamber, plus the regulator and hose to feed it. Leak-test every joint with soapy water before first light.
3/4 in naturally-aspirated forge burner
3/4 in
- BTU/hr
- 90,000
- Burners
- 1
- Regulator
- 0-30 PSI
Heats roughly 300-350 cu in of chamber. The default single-burner size for a first forge. Needs a 0-20 or 0-30 PSI regulator.
1 in high-output forge burner
1 in
- BTU/hr
- 150,000
- Burners
- 1
- Regulator
- 0-30 PSI
Feeds a larger chamber (up to ~700 cu in) or reaches welding heat. Hungrier - pair with a 30/40 lb tank to avoid freeze-up.
Blown (ribbon) forge burner
forced-air
- BTU/hr
- 120,000
- Burners
- 1
- Regulator
- 0-30 PSI
A fan feeds air for even, controllable heat and easy welding, but needs power and more setup than a naturally-aspirated burner.
Adjustable propane regulator 0-30 PSI
POL/QCC-1 fitting
- Regulator
- 0-30 PSI
0-30 PSI range reaches forge-welding pressure. Confirm the tank fitting (QCC-1) matches your tank.
Adjustable propane regulator 0-20 PSI
POL/QCC-1 fitting
- Regulator
- 0-20 PSI
Fine for general forging heat. If you plan to forge-weld, choose the 0-30 PSI version instead.
Propane hose and 0-30 PSI regulator kit
10 ft hose
- Regulator
- 0-30 PSI
Complete gas train for most forges. Leak-test every joint with soapy water before first light.
Propane regulator, hose and gauge kit
8 ft hose
- Regulator
- 0-30 PSI
Includes a pressure gauge so you can set PSI repeatably. Verify the hose is rated for LP gas, not air.
Line it to hold the heat
BTU only matters if the chamber keeps its heat. Insulate before you worry about a bigger burner.
Ceramic fiber blanket, 1 in x 8 lb density
1 in thick, 2300-2600F
- Material
- Ceramic Fiber
The standard forge liner. ALWAYS rigidize and coat it - loose ceramic fibers are a respiratory hazard. Wear a respirator when cutting.
Ceramic fiber blanket, 2 in x 8 lb density
2 in thick, 2300-2600F
- Material
- Ceramic Fiber
Two inches of wall holds heat and gas better and cuts propane use. Same safety rules: rigidize, coat, and never breathe the dust.
Frequently asked questions
How many BTU does a propane forge need?
It depends on chamber size. A small knife forge around 350 cubic inches needs roughly 90,000 BTU/hr from a single 3/4 inch burner. Double the volume and you roughly double the heat needed. Enter your chamber's dimensions above for a specific figure, and add about 25% if you plan to forge weld.
What size burner do I need for my forge?
As a rule of thumb, one 3/4 inch naturally-aspirated burner heats about 350 cubic inches of chamber, and a 1 inch burner about 700. If your chamber is bigger, use multiple burners or a larger one. Good insulation matters as much as burner size - a leaky forge behaves like a much bigger one.
How many burners should a forge have?
Roughly one 3/4 inch burner per 350 cubic inches of interior. Most beginner knife forges run a single burner; general-purpose forges with longer chambers use two. More burners mean more even heat over length but roughly proportional propane use, so match the count to your chamber and your work, not to horsepower bragging.
Can I build my own forge burner?
Yes - simple naturally-aspirated ("Frosty T" or similar) burners are a common DIY project and can work well. But burner tuning affects flame chemistry and safety, so follow a proven design exactly, test outdoors, and check for a stable, neutral flame. If you are not comfortable with gas fittings, a ready-made burner is a safer starting point.