A 20 gallon propane tank typically holds around 4.7 gallons of liquid propane when full. This equates to approximately 18-20 pounds of propane. The exact weight will depend on the temperature and pressure inside the tank.
Quick Answer
A standard 20 gallon propane tank holds approximately 18-20 pounds of propane when full.
Propane Weight per Gallon
Propane is a liquid fuel that is stored under pressure in tanks. One gallon of liquid propane weighs approximately 4.2 pounds. This means that the total weight of propane in a full 20 gallon tank can be calculated as:
20 gallons x 4.2 pounds per gallon = 84 pounds
However, propane tanks are not filled completely full with liquid. A portion of the tank’s volume is left as vapor space to allow for expansion and contraction of the liquid propane with temperature changes.
Typical Fill Levels
A standard 20 gallon propane tank is filled to around 80% capacity with liquid propane. This leaves about 4 gallons of empty space for the propane vapors.
At 80% fill capacity:
0.80 x 20 gallons = 16 gallons of liquid propane
With a density of 4.2 lbs per gallon, 16 gallons of propane weighs:
16 gallons x 4.2 lbs/gallon = 67.2 pounds
So if filled to 80% capacity, a 20 gallon propane tank would contain about 67 pounds of liquid propane.
Adjusting for Temperature
The density of propane, and therefore its weight per gallon, changes slightly based on temperature. At higher temperatures, the density decreases very slightly. Typically, propane tanks are filled based on a reference temperature of 60°F.
The density of propane at 60°F is 4.2 lbs/gallon. At 80°F, the density drops to around 4.15 lbs/gallon. So during the hot summer months, the weight of propane in a full 20 gallon tank would be a bit less.
Typical Fill Weights
Taking into account the reduced fill level and warmer temperatures, a standard 20 gallon propane tank typically contains between 18-20 pounds of propane when filled:
- At 80% fill capacity: 67.2 x 0.96 (density adjustment) = 18 pounds
- At 90% fill capacity: 76.8 x 0.96 = 20 pounds
So you can expect around 18-20 pounds of propane in a full 20 gallon tank during most conditions.
Checking the Tank Gauge
Another way to verify how full your propane tank is by checking the float gauge on top of the tank. This gauge displays an approximate percentage fill level:
- 100% full reading indicates around 20 lbs of propane
- 80% reading indicates around 16 lbs
- 50% reading indicates around 10 lbs
So you can get a quick visual on roughly how many pounds of propane are left before your next refill. Just remember that the gauge is not extremely precise – an 80% reading could correlate to 16-18 lbs.
Refilling 20 lb Tanks
When you exchange or refill a standard 20 lb propane tank, you are typically getting about 17-18 pounds of propane added back into the empty cylinder. The exact amount can vary slightly depending on who is filling it and the procedures they follow.
Sometimes you may get up to the full 20 pound capacity restored, but don’t expect to get a precise 20 pounds each time. Anywhere from 17-20 lbs is normal when refilling a 20 gallon tank.
30 lb Tanks
There are also some larger 30 lb propane tanks used for RV and barbecue applications. These hold approximately 7.5 gallons of liquid propane when full. With a density of 4.2 lbs/gallon, a full 30 lb propane tank contains about:
7.5 gallons x 4.2 lbs/gallon = 31.5 pounds
Adjusting for the 80% fill level, temperature, and other factors, you can expect approximately 25-28 pounds of propane in a refilled 30 lb cylinder.
Checking Liquid Level
You can also check the liquid level directly using a dip stick gauge. This consists of a stick that you slide into the tank’s valve to measure the depth of liquid propane. Matching the liquid depth against the tank’s diameter provides the volume.
Each gallon of liquid propane weighs 4.2 lbs, so you can calculate the approximate weight based on the measured liquid volume. This gives the most precise weight measurement versus relying on the tank gauge.
However, be very careful when using a dip stick – only insert it into the tank’s valve using proper procedures. Propane is highly flammable and pressurized.
Propane Tank Sizes
Propane tank sizes are measured in gallons, but the standard ratings refer to water gallons not actual liquid propane gallons contained. Here are some common propane tank sizes and capacities:
| Tank Size | Propane Capacity (lbs) |
| 5 gallons | 10 pounds |
| 10 gallons | 18 pounds |
| 20 gallons | 18-20 pounds |
| 30 gallons | 25-28 pounds |
| 40 gallons | 35 pounds |
| 100 gallons | 87 pounds |
So check the tank rating in gallons, then refer to the table for an estimate of how many pounds of propane it can hold when full.
Propane Consumption
Knowing how many pounds of propane are in your tank allows you to estimate how long it will last based on your usage. Here are some approximations for consumption from various propane appliances:
- Gas grill – 0.2 – 0.5 lbs/hour
- RV furnace – 1 – 2 lbs/hour
- Outdoor patio heater – 2 – 4 lbs/hour
- Whole house heating – 4 – 8 lbs/hour
Multiply your typical hourly usage by the number of pounds in the tank to get a rough runtime. For example, grilling for 4 hours with a 20 lb tank would use approximately:
0.5 lbs/hr x 4 hours = 2 pounds
Leaving around 18 pounds remaining, for approximately 36 more hours of grilling time.
Refills and Exchanges
Once your propane tank runs low, you have a couple options to get more fuel:
- Refill – Bring the same tank back to get refilled. This is the most cost effective option.
- Exchange – Swap out your empty tank for a full replacement. More convenient but costs more per pound.
Many retailers like grocery stores, gas stations, and hardware stores offer propane tank exchange programs. Or you can go directly to a propane supplier to get your tank refilled.
Safety Tips
Always handle propane tanks with care, as propane is highly flammable and pressurized:
- Transport and store upright and secured
- Keep away from heat, sparks, and open flames
- Check for leaks and damages before refilling
- Only refill to 80% capacity
- Follow local codes and standards for storage and use
Taking proper safety precautions will allow you to securely use propane and get the most out of each tank.
Conclusion
A standard 20 gallon propane tank holds about 4.7 gallons of liquid propane when full. With propane weighing around 4.2 pounds per gallon, this equates to approximately 18-20 pounds of propane depending on the fill level.
Understanding tank sizes, propane densities, and fill levels allows you to estimate the weight of propane you are getting when exchanging or refilling tanks. This helps ensure you get the full value and usage out of your propane fuel purchase.