How Many Gallons of Propane in a 100 lb Tank? (2026)

October 14, 2026 admin

Quick Answer: A 100 lb propane tank holds approximately 23.6 gallons of propane. However, propane tanks are only filled to 80% capacity for safety, so you’ll actually get about 18.9 usable gallons from a “full” 100 lb tank.

Understanding Propane Tank Sizes

Propane tanks are named by the weight of propane they hold, not the volume. This confuses many people. Here’s the key conversion:

1 gallon of propane weighs 4.24 pounds

So for a 100 lb tank:
– 100 ÷ 4.24 = 23.6 gallons (total capacity)
– 23.6 × 0.80 = 18.9 gallons (usable, at 80% fill)

Why Only 80% Full?

Propane expands significantly with temperature. The 80% fill rule (called the ” outage”) leaves room for expansion on hot days. Without this safety margin, pressure could build to dangerous levels. This is law – your propane supplier will never fill beyond 80%.

Common Propane Tank Sizes Compared

| Tank Size | Total Gallons | Usable Gallons (80%) | Typical Use |
|—|—|—|—|
| 20 lb (BBQ tank) | 4.7 gal | 3.8 gal | Grills, patio heaters |
| 30 lb | 7.1 gal | 5.7 gal | RVs, campers |
| 40 lb | 9.4 gal | 7.5 gal | RVs, food trucks |
| 100 lb | 23.6 gal | 18.9 gal | Home heating supplement, workshops |
| 250 gal (bulk) | 250 gal | 200 gal | Whole-home heating |
| 500 gal (bulk) | 500 gal | 400 gal | Large homes, farms |

How Long Will a 100 lb Tank Last?

It depends entirely on what you’re powering. Propane contains 91,500 BTU per gallon.

Estimated Runtime (18.9 usable gallons = ~1,729,350 BTU)

Real-world example: Using a 30,000 BTU space heater for 8 hours a day, a 100 lb tank lasts about 7 days.

100 lb Tank Dimensions and Weight

Height: ~48 inches (4 feet)
Diameter: ~15 inches
Empty weight (tare): ~70 lbs
Full weight: ~170 lbs (70 + 100 lbs of propane)
DOT certification: Must be recertified every 10 years

At 170 pounds full, you’ll need help moving it or a dolly!

Cost to Fill a 100 lb Tank

Prices vary by region and season:
– Average: $3.00-$4.50 per gallon
– Fill cost: 18.9 gal × $3.50 = ~$66
– Winter prices are typically 20-30% higher than summer
– Bulk/contract pricing can save 10-20%

Money-saving tip: Fill up in summer when prices are lowest, if you have safe storage.

Safety Tips for 100 lb Tanks

Always transport upright – never on its side
Secure during transport – prevent rolling or tipping
Store outdoors – never in an enclosed space, basement, or garage
Keep away from heat – at least 10 feet from ignition sources
Check for leaks – use soapy water on connections (bubbles = leak)
Know the smell – propane has a rotten-egg odor added (ethyl mercaptan)
Check the date – tanks need recertification every 10 years

Refilling vs. Exchanging

Unlike 20 lb BBQ tanks (which you often exchange), 100 lb tanks are typically refilled at:
– Propane dealers
– U-Haul locations
– Tractor Supply Co.
– Ferrellgas / AmeriGas distributors
– Some hardware stores

Call ahead – not every location can fill 100 lb tanks.

Frequently Asked Questions

Can I lay a 100 lb propane tank on its side? No. Propane tanks must remain upright. Laying them down can cause liquid propane (instead of vapor) to enter the regulator, creating a dangerous situation.

How do I know how much propane is left? Use the hot water method: pour hot water down the side, then feel for the cold line (propane level). Or buy an inline propane gauge.

Does propane go bad? No! Propane doesn’t degrade like gasoline. It lasts indefinitely in a properly maintained tank.

Can I use a 100 lb tank for my home? Yes, for supplemental heating, cooking, or hot water. For whole-home primary heating, a larger bulk tank (250+ gallons) is more practical.

Conclusion

A 100 lb propane tank holds 23.6 gallons total, with 18.9 usable gallons at the safe 80% fill level. Whether you’re heating a workshop, running a food truck, or supplementing home heat, understanding your tank’s real capacity helps you plan refills and budget fuel costs. Stay safe, buy in summer, and always respect the 80% rule!

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