How To Tell If Propane Tank Is Empty? (Or How Much Is Left?)

You can tell if a propane tank is empty or not. Even more, you can tell exactly how much propane is left in a propane tank. Looking at the propane tank itself, however, it’s not all that obvious how to tell if the propane tank is empty or how many lbs or gallons is left in the tank.

A propane tank is not like a wine barrel. You can’t just knock on the propane barrel to check if it’s empty. Even if you would hear a hollow sound, there still might be 1 lb, 2 lbs, or 5 lbs of propane in 20 lbs propane tank. Knocking is just not the way.

We use two methods to tell if the propane tank is empty. The same two methods can also be used to tell how much propane is left in a propane tank. These two methods are:

1. Weighing a propane tank. This is the simplest way how to tell if a 20 lb or 100 lb propane tank is empty. You just need a scale and use a little bit of math (we will explain exactly how to weigh a propane tank and calculate how much propane is left in there).

   

2. Using an HVAC gauge. If you have a big 100-gallon, 250-gallon, 500-gallon, or 1,000-gallon propane tank, you can’t really put it on a scale, right? That’s why HVAC professionals use an HVAC gauge to tell how much propane is in a big residential tank. Most of these 100-1,000 gallon propane tanks already have this gauge installed; you can just check how much propane is in there just by checking the gauge (it works like a fuel tank gauge).

   

Example Of Using Weighing Method: How to tell if a 20 lb propane tank is empty? First, check how much does a 20 lb propane tank weigh when empty (it’s written on the label). An average aluminum 20 lb propane tank weighs 13.5 pounds. This is your tare weight (weight of an empty tank). If you put such a 20 lb propane tank on a scale and it weighs 13.5 pounds, the 20 lb propane tank is empty.

How to tell how much propane is left in this 20 lb propane tank? A 20 lb propane tank holds 16 lb of propane when full (the 80% safety rule). Let’s say you put this tank on the scale and the scale says 21.5 lb. That’s a 13.5 lb empty tank + how much propane? 8 lb of propane. That means that your 20 lb propane tank is half full (or half empty, it’s the optimist vs pessimist view).

Your 20 lb propane tank might not have an empty weight of 13.5 lb. You might want to know how to tell if 50 lb, 100 lb, or any other capacity tank is empty, or how much propane it has left.

We will explain exactly how to use the weighing method to tell how much propane is still left in a propane tank. To help everybody out, we have designed a ‘Propane Tank Percentage Calculator’ that automatically tells you how many percent of propane is still left in your tank. You just have to input three things:

1. Propane tank capacity. Example: 20 lb.
2. Weight of empty tank. We will look at a chart of how much empty propane tanks weigh (10 lb, 20 lb, 50 lb, 100 lb, and so on).
3. Current propane tank weight. You just put the tank on a scale and input the pounds into the calculator.

We will also look at how you can use the HVAC gauge method to tell how much propane is left in the tank, and address a questionable ‘Use warm water’ method of telling if the propane tank is empty.

Weighing Propane Tank To Tell If It Is Empty (Method 1)

Here is all you need for this method: Your propane tank + scale.

The weight the scale will show is the summary of the empty propane tank + whatever propane is left in the tank. Here is how we can write this formula:

Weight (Scale) = Weight Of Empty Propane Tank + Weight Of Leftover Propane

Here is how to tell that the propane tank is empty: Weight on the scale is the same as the weight of the empty propane tank.

The step-by-step process of how to tell if a propane tank is empty:

1. Check the weight of an empty propane tank. This weight is written on the propane tank. You can check roughly how much empty propane tanks weigh here. Write that number down.
2. Put a propane tank on the scale. Write down the number on the scale.
3. If the numbers are the same (or there is up to a 5% deviation), the propane tank is empty.
4. If the weight on the scale is larger than the weight of an empty propane tank, the tank is not empty yet (we will calculate how much propane is left further on).

Example: Let’s say you have a 20 lb steel propane tank. On the label, under ‘Tare Weight’, it says ’18 lb’. That means that an empty steel propane tank weighs 18 lb. You weigh it; the scale says 18.6 lb. That is within the 5% deviation and this propane tank is empty (or there is very little propane left in it).

Now, what happens in the scale says 25 lbs? That means that some propane is still in the propane tank. How much exactly? We can calculate that:

How To Tell How Much Propane Is Left In The Tank

Alright, if we have a 20 lb tank that weighs (empty weight) 18 lb and it weighs 25 lb, that clearly means that you have 7 lb of propane left in the tank.

Here is the important part:

For safety reasons, all propane tanks are filled up to 80% of their capacity. That means that a full 20 lb propane tank holds 16 lb of propane, a full 100 lb propane tank holds 80 lb of propane, a full 500-gallon tank contains 400 gallons of propane, and so on.

Example: If we have a 20 lb propane tank with an empty weight of 18 lb, and we fully fill it, it won’t weigh 38 lb. Its full weight will be 34 lb because there is not 20 lb of propane in a 20 lb propane tank; there is only 16 lb of propane in a fully filled propane tank.

Here are examples of how much propane is left in a 20 lb tank with an empty weight of 18 lb:

• Scale weight = 18 lb. This propane tank is empty; it contains 0% of propane.
• Scale weight = 19 lb. This propane tank still has 1 lb of propane left; it’s about 6% full tank.
• Scale weight = 20 lb. This propane tank still has 2 lb of propane left; it’s about 13% full tank. You still have 1/8 of the tank left.
• Scale weight = 21 lb. This propane tank still has 3 lb of propane left; it’s about 19% full tank.
• Scale weight = 22 lb. This propane tank still has 4 lb of propane left; it’s about 25% full tank. You still have a quarter of the tank left (1/4).
• Scale weight = 23 lb. This propane tank still has 5 lb of propane left; it’s about 31% full tank.
• Scale weight = 24 lb. This propane tank still has 6 lb of propane left; it’s about 38% full tank.
• Scale weight = 25 lb. This propane tank still has 7 lb of propane left; it’s about 44% full tank.
• Scale weight = 26 lb. This propane tank still has 8 lb of propane left; it’s about 50% full tank. You still have half of the tank left (1/2).
• Scale weight = 27 lb. This propane tank still has 9 lb of propane left; it’s about 56% full tank.
• Scale weight = 28 lb. This propane tank still has 10 lb of propane left; it’s about 63% full tank.
• Scale weight = 29 lb. This propane tank still has 11 lb of propane left; it’s about 69% full tank.
• Scale weight = 30 lb. This propane tank still has 12 lb of propane left; it’s about 75% full tank. You still have three-quarters of the tank left (3/4).
• Scale weight = 31 lb. This propane tank still has 13 lb of propane left; it’s about 81% full tank.
• Scale weight = 32 lb. This propane tank still has 14 lb of propane left; it’s about 88% full tank.
• Scale weight = 33 lb. This propane tank still has 15 lb of propane left; it’s about 94% full tank.
• Scale weight = 34 lb. This propane tank still has 16 lb of propane left; it’s about 100% full tank. This is the weight of a full tank.

We hope this makes sense. It might a bit complex, however; to help you out calculate exactly how many percent of the propane is left in the tank, we have developed a calculator that automatically calculates how many lb of propane are still left in the tank. Here is the calculator:

Propane Tank Percentage Calculator

Here is how you can use this calculator to determine how many pounds of propane you have left in the tank:

Let’s say you have a 100 lb propane tank. You read the weight of an empty 100 lb tank on the label; let’s say it’s 70 lb. You put the tank on the scale and you can see that it weighs 88.2 pounds. If you slide the first slider to ‘100’, the second slider to ’70’ and the third slider to ‘88.2’, you get that there is still 23% of propane left in the tank. You have about a quarter of propane left.

You can use this calculator to check the percentage of propane left in any 100 lb or smaller tank. If you need help with the calculations, you can use the comments below and we’ll help you out.

Using HVAC Gauge To Tell If Propane Tank Is Empty (Method 2)

If your propane tank has an HVAC gauge mounted on the top, you can simply read off how much propane is left in the tank.

Bigger residential tanks will usually have the gauge pre-installed. For example, if you want to know if a 100-gallon, 250-gallon, 500-gallon, or 1,000-gallon propane tank is empty, you don’t weigh it. You just check the gauge, installed on the tank. The gauge will also tell you how much propane you still have left in the tank.

In most cases, the gauge will not tell you exactly how many gallons are left in the 100, 250, 500, or 1000 propane tank. Here is a neat table of how many gallons are left in these tanks:

Example: If a gauge on the 500-gallon tank says 1/4 capacity, you still have 100 gallons of propane left in the tank.

In short, if you have a pre-installed gauge on the propane tank, you can easily tell how much propane is left in the tank.

Let’s also address a bit controversial method of telling if the propane tank is empty or not:

‘Warm Water’ Method Explained

Supposedly, one way to tell if there is still propane left in the tank is by pouring warm water down the length of the tank.

The method tells you that:

1. If the water temperature doesn’t change much, the propane tank is empty.
2. If the water temperature decreases (you can cold water at the end), the propane tank is not empty yet.

Again, supposedly, the presence of propane in the tank should cool the water. The problem with this method is that it really is not all that accurate.

Namely, propane inside the tank will cool the water a bit, yes. However, the propane tank itself (be it steel or aluminum) will mostly cool the water. That’s because the metal propane tank is made out of has very good heat transfer properties, and if you pour warm water on metal at a lower temperature, the water will be cooled.

That usually means that you get colder water at the bottom of the propane tank, regardless if the tank is full or empty.

All in all, telling if the propane tank is empty or how much propane is left in the propane tank is not hard at all if you have a pre-installed gauge mounted on the tank.

Even if you don’t, your go-to method is to weigh the tank and calculate a bit. If you need some help with the calculations, you can always turn to us, use the comments below and we’ll try to help you out.