Is a 20 lb propane tank 5 gallons?

Quick Answer

No, a standard 20 lb propane tank does not contain exactly 5 gallons of propane. While propane tanks are often referred to by the pound capacity, the actual amount of liquid propane they can hold varies based on temperature and pressure. At 60°F, a 20 lb propane tank can hold around 4.5 gallons of liquid propane. The exact capacity may be slightly more or less depending on specific conditions.

How Much Liquid Propane Can a 20 lb Tank Hold?

The capacity of a propane tank is measure in pounds (lbs) of propane. However, when considering how much liquid propane will fit in a tank, the volume must be measured in gallons. Here are some key facts about 20 lb propane tank capacities:

– At 60°F a 20 lb propane tank can hold approximately 4.5 gallons of liquid propane. This is considered the standard capacity.

– At 100°F that same tank can hold around 4.2 gallons of liquid. Capacity is reduced at higher temperatures.

– At 35°F the tank can hold up to 4.7 gallons of liquid propane. Colder temperatures allow more liquid gas to fit.

– When the tank is filled to 80% capacity at 60°F, it will have approximately 3.6 gallons of liquid propane available. This is considered the safe usable capacity.

– Tank volumes are based on the liquid gallons. Propane expands 270 times from liquid to gas form.

So while the tank may be stamped as a 20 lb tank, the actual amount of propane fuel inside varies based on the temperature and fill level. Under normal conditions of 60°F and 80% fill, expect around 3.6 gallons of liquid propane in a 20 lb tank.

Why Propane Tank Capacity Varies

The main reason that a 20 lb propane tank does not have exactly 5 gallons of capacity is because propane is compressed into a liquid form inside the tank. The amount of liquid fuel that can fit depends on the pressure and temperature conditions. Here are some key reasons why capacity varies:

– Propane is a gas at normal temperatures and pressures. To store more fuel in a smaller tank, it is compressed into a liquid which takes up less space.

– Liquids expand when heated and contract when cooled. Warmer temperatures mean less liquid propane can fit inside the tank.

– Propane tanks have a safe maximum pressure rating. More liquid can be safely compressed at lower temperatures and pressures.

– At constant pressure, temperature changes have the biggest impact on liquid volume. Pressure changes impact capacity to a lesser degree.

– Tanks are not filled to 100% capacity, only around 80% full for safety and to allow for expansion. This further reduces usable liquid volume compared to total volume.

– Reading gallons requires a fixed temperature reference point. 60°F is commonly used to rate standard tank capacity in gallons.

So in summary, propane capacity varies based on temperature, pressure, liquid expansion properties, tank pressure ratings, fill levels, and volume reference conditions. All these factors mean a 20 lb tank ends up holding around 4.5 gallons when you account for real-world conditions.

Standard 20 lb Propane Tank Dimensions

In addition to weight and volume capacity, the standard physical dimensions of 20 lb consumer propane tanks are good to know:

– Total height: 17.75 inches

– Diameter: 12.75 inches

– Footring diameter: 14 inches

– Tare weight (empty): 18 lbs

– Gross weight (when full): 38 lbs

– Volume capacity at 60°F: 4.5 gallons (approx.)

– Water capacity: 24.5 litres (6.5 gallons)

– Pressure when full: 130 psi

– Construction: Powder coated steel or aluminum

– Valve type: OPD (overfill protection device)

– Connector: Type 1 cylinder valve

– Certification: DOT (Dept of Transportation)

So a typical 20 lb propane cylinder will be about 18 inches high and 13 inches diameter. The main specifications like the 4.5 gallon 60°F volume capacity are based on common industry standards. Tank sizes, valve types, and certifications are regulated to ensure safety and consistency across brands.

What 20 lb Tanks are Used For

Some of the most common uses for standard 20 lb propane tanks include:

– Gas grills – The small size makes them convenient for grill mobility.

– Outdoor fire pits – Easily portable for outdoor fire features.

– RV appliances – RVs use propane for stoves, fridges, and heating.

– Construction heaters – Portable propane heaters are commonly used on job sites.

– Emergency generators – Run small generators using 20 lb propane tanks.

– Backyard mosquito control – Propane helps power mosquito misters.

– Food trucks – Onboard propane tanks for food truck ovens and grills.

– Catering – Easily transport propane for catering and outdoor events.

– Crop spraying – Mounted propane heaters for crop protection.

– Forklifts – Can use propane instead of gasoline.

– Roofing kettles – Melting asphalt or tar.

– Smokers – Propane-powered smoker boxes.

– Floor stripper machines – Heats water to steam floors.

The small portable size and energy density of propane makes 20 lb cylinders useful for many applications. They can be easily exchanged and transported as needed.

Propane Tank Sizes and Ratings

Beyond just 20 lb tanks, consumer propane cylinders are available in several standard sizes with different capacities:

Tank Size Empty Weight Filled Weight Lbs Propane Gallon Capacity
5 gallon 8 lbs 23 lbs 15 lbs 3.5 gal
10 gallon 12 lbs 37 lbs 25 lbs 6.0 gal
20 pound 18 lbs 38 lbs 20 lbs 4.5 gal
30 pound 28 lbs 58 lbs 30 lbs 7.5 gal
40 pound 32 lbs 72 lbs 40 lbs 10.5 gal
100 pound 63 lbs 163 lbs 100 lbs 24 gal

– Tank tare weights when empty range from 8 – 63 lbs depending on size.

– Common sizes include 5, 10, 20, 30, and 40 pound tanks for small scale consumer use.

– Larger 100 lb tanks are also available but used more commercially.

– The pound rating correlates to the pounds of propane when full.

– Gallon capacities are approximate based on 60°F reference.

– All tanks have pressure relief valves for safety.

Larger tanks contain more propane fuel, but smaller tanks are more portable and suited to applications like grilling, RV use, etc. The 20 lb tank provides a good balance of compact size with adequate runtime.

Refilling 20 lb Propane Tanks

When your 20 lb propane tank runs out you will need to get it refilled. Here are some tips on refilling:

– Only go to qualified propane refilling locations. Many gas stations, RV dealers, and hardware stores offer refilling services.

– Make sure personnel have training on properly handling tanks.

– They will weigh the tank to see how many pounds need filling. Typically this will be around 17-18 lbs on an empty 20 lb tank.

– Tanks are refilled by weight, not volume. So you pay for the pounds of propane, not number of gallons.

– Cost is around $2-$3 per pound. So a full 20 lb refill may cost $40-$60.

– Only fill to 80% capacity for safety and expansion room. This is around 15-16 lbs of propane.

– Older tanks must be recertified after 12 years, ensuring they are safe for continued use.

– Damaged or heavily rusted tanks should not be refilled. Ask about exchanging for a new tank.

– Never transport or store propane tanks inside a hot vehicle.

Following proper refilling procedures is critical to safe operation. Only go to qualified filling stations and be sure to keep the receipt showing the tank has been properly examined and filled by certified personnel.

Switching to Refillable Propane Tanks

Many consumers use disposable 1 lb propane canisters for grilling. While convenient, these produce more waste and have higher per-pound costs. Switching to refillable 5 or 20 pound tanks offers these benefits:

– 1 lb canisters cost over $5 per pound of propane fuel. 20 lb tanks average only $2-$3 per pound to refill.

– No need to constantly dispose of canisters that end up in landfills.

– Refillable tanks have lower long-term costs.

– No need to keep buying new 1 lb canisters.

– More convenient with larger capacity and fewer tank changes.

– Easy to take and refill a 20 lb tank at local refilling stations.

– More secure connection to grill or appliance.

– OPD valves automatically stop propane flow if there is a leak.

– Smaller tanks more prone to tipping over than larger 20 lb tanks.

For occasional grilling the 1 lb cans may still be suitable. But for anyone who grills frequently or in higher volumes, the 20 lb refillable tanks make the most sense economically and environmentally. Just be sure to follow safe storage, transport, and refilling guidelines.

Propane Tank Storage Tips

It is important to properly handle and store propane tanks when not in use:

– Disconnect all hoses and fittings when storing. Install protective cap over valve.

– Check for any leaks or corrosion before storage. Damaged tanks should not be used.

– Do not store in enclosed spaces like a car, garage, basement, or shed. Tanks must be outdoors.

– Keep away from heat or flame sources. Avoid storing in direct sunlight.

– Position tank upright and secure it from falling over.

– Do not let children play around stored tanks. Keep in locked enclosure if needed.

– Turn off all appliance pilot lights if storing propane tanks indoors for appliance use.

– Keep spare tanks outdoors in upright position. Limit to 2 spare tanks.

– Mark empty tanks with chalk or grease pencil so they aren’t mistaken as full.

Proper propane tank storage in cool outdoor areas will help ensure safety and reliable performance. Take care to prevent damage, leaks, tipping, or exposure to direct heat sources.

Safety Tips for 20 lb Propane Tanks

Beyond proper filling, storage, and handling, these are some other key safety tips for consumer propane tanks:

– Inspect tank and valves regularly for damage, rust, or leaks

– Follow all manufacturer guidelines for transport and use

– Ensure appliances are suited for propane fuel

– Confirm seals, gaskets, hoses and fittings are undamaged

– Position tank upright and secure when using with appliances

– Keep at least 10 feet away from tents, other people, or flammable objects

– Turn off tank valve when not in use

– Never use near open flames or sources of heat

– Avoid storing or placing near furnace or water heater exhaust

– Do not smoke or have open flames near operating tank

– Watch for venting gas which signals a leak

– Know how to check for leaks with soapy water solution

– Never use damaged or expired tanks

– Children should not handle or operate tanks

– Install carbon monoxide detectors in RV or other enclosed spaces using propane

Following basic safety protocols when using 20 lb propane tanks will help avoid accidents or dangerous situations. Be sure to read and adhere to all warning labels and manufacturer guidelines for your tank.


While 20 lb propane tanks are a convenient compact size, they do not actually hold exactly 5 gallons when filled. Due to temperature, pressure, and expansion variables, the actual capacity is around 4.5 gallons under typical conditions. Understanding how tank sizes, ratings, and capacities relate is helpful for choosing the right propane fuel source. Following manufacturer guidelines, inspecting equipment, proper handling and storage, and using qualified filling stations will ensure safe and reliable usage of 20 lb propane cylinders for your applications.

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