Colin Snow
The volume of a sleeping bag is important to know when considering the size of the stuff sack required to store it. The volume of a sleeping bag can be calculated by measuring the bottom diameter of the bag, finding the circle area, and multiplying it by the height. Sleeping bags filled with down are more compressible than synthetic-filled ones and require lesser volume stuff sacks. If you are backpacking, you will want to compress your sleeping bag as much as possible to save space in your backpack. A rule of thumb is to take the compressed volume of your sleeping bag and add 5 litres to determine the required volume of the compression sack.
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What You'll Learn
Measure the bottom diameter, find the circle area, and multiply by the height
To determine the volume of your sleeping bag in litres, you can use the formula: "Measure the bottom diameter, find the circle area, and multiply by the height".
Firstly, you need to measure the bottom diameter of your sleeping bag. The diameter is the line that crosses the centre of the circle and touches both of its margins.
Next, you need to find the circle's area. The circle area is calculated using the diameter or radius of the circle. The radius is the line that begins at the centre of the circle and ends at the circle's margin. The diameter of a circle is twice the length of its radius, so to find the radius, divide the diameter by two. The formula for finding the area of a circle is: circle area = π x (diameter/2)^2, where π is approximately 3.14.
Finally, multiply the circle area by the height of the sleeping bag to get the volume in cubic centimetres. To convert cubic centimetres to litres, divide the volume by 1000.
It is important to note that this method assumes the sleeping bag is compressed into a cylindrical shape. The volume of a sleeping bag can vary depending on how tightly it is compressed and the shape of the container. Additionally, the fit of a sleeping bag is also an important consideration, as it should be snug but not too tight, and the length, shoulder girth, and hip girth should be taken into account when choosing a sleeping bag.
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Compressibility depends on the filling
To determine the volume of your sleeping bag in litres, you can measure the bottom diameter of the bag, find the circle's area, and multiply that by the height. Alternatively, you can simply stuff the sleeping bag into its container bag and measure the volume.
The compressibility of a sleeping bag depends on its filling. Sleeping bags typically have either a down (natural) or synthetic fill. Good-quality down has the best warmth-to-weight ratio and is highly compressible. Down sleeping bags are usually more expensive, and they require careful handling. When down gets wet, it loses most of its insulation value and takes a long time to dry. Some manufacturers treat their down with a durable water-repellent (DWR) finish to mitigate this issue.
Synthetic fill is easier to clean, maintains greater insulation when wet, and is more affordable than down. However, synthetic bags are slightly bulkier, heavier, and may have a shorter lifespan. Synthetic insulation typically uses materials like Polarguard 3D or Primaloft, with the former being more durable and the latter offering lighter and more compressible insulation.
The filling's "loft" or "fluffiness" is another factor influencing compressibility. Loft is a measure of the volume taken up by a given weight of filling. A higher loft means the filling takes up more space and traps air more efficiently, resulting in better insulation. Therefore, a sleeping bag with a high loft will be less compressible.
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Use a bucket to measure volume
If you want to determine the volume of your sleeping bag in litres, one method is to use a bucket. This method is useful if you don't have a compression sack or stuff sack to hand.
First, stuff your sleeping bag into the bucket. It may be helpful to compress the bag as much as possible before placing it in the bucket, as you would when using a compression sack. Ensure the bag is packed tightly and evenly, with no air gaps.
Once the bag is in the bucket, you can measure the volume of the remaining space. Fill the bucket with water, measuring the amount of water it takes to fill the bucket to the top of the sleeping bag. This will give you the volume of your sleeping bag.
You can also try using a similar container, such as a large pot, if you don't have a bucket available. Alternatively, you can use a measuring cylinder, which will give you a more precise volume reading.
This method provides a simple way to estimate the volume of your sleeping bag without the need for complex calculations. It is worth noting that the volume of your sleeping bag can vary depending on how tightly it is compressed and the method used to store it. For example, a sleeping bag compressed in a cylinder shape will have a different volume compared to one that is simply stuffed into a bag.
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Add 5 litres to the compressed volume
The best way to determine the number of litres your sleeping bag takes up is to measure its compressed volume and add 5 litres. This will give you the minimum volume of the compression sack you need.
Firstly, you need to measure the volume of your sleeping bag. To do this, place your sleeping bag in a cardboard box that is larger than the bag. Press the sleeping bag down firmly until the upper surface is roughly level in the box (the bag is now mildly compressed). Measure the average depth that the bag occupies in centimetres or inches. If you are measuring in centimetres, divide the total by 1000 to calculate the volume in litres. If you are measuring in inches, multiply the length x width x depth to get the volume in cubic inches, then divide by 61 to give the volume in litres.
Alternatively, you can measure the bottom diameter of the bag, find the circle area and duplicate this with the height to get the approximate volume.
Now that you have the volume of your sleeping bag, add 5 litres to this number. This will give you the minimum volume of the compression sack you need. For example, if your sleeping bag has a compressed volume of 5.3 litres, you will need a compression sack of at least 10.3 litres.
It is important to note that sleeping bags vary in their packed volume depending on the type of insulation and the shell and liner fabrics they use. Therefore, it is not possible to simply equate a bag temperature rating with a compression sack size. If you are backpacking, you will want to compress your sleeping bag as small as possible to save space in your backpack. However, if you are car camping, it is unnecessary to compress your sleeping bag too much, as you will have more space to work with.
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A stuff sack is not always necessary
When it comes to packing a sleeping bag, the use of a stuff sack is a matter of personal preference and depends on various factors, including the type of bag, the activity, and space optimisation. While a stuff sack can provide benefits, it is not always necessary, and there are alternative methods to consider.
One key consideration is the type of sleeping bag. If you have a down bag, keeping it dry is a top priority. In this case, a stuff sack, particularly a waterproof one, can be advantageous. It ensures the bag stays dry, especially during activities like creek crossing where there is a risk of total immersion in water. Additionally, a stuff sack can provide an extra layer of protection from the elements, keeping your bag safe and dry during transportation.
However, it's important to note that using a stuff sack can sometimes result in inefficient use of space. A sleeping bag is often one of the most flexible items in your pack. By compressing it into a stuff sack, it may no longer be able to fill the voids created by less flexible items, ultimately taking up more space in your bag. In such cases, it might be preferable to let the sleeping bag fill out the available space first and then compress it by placing other items on top. This approach ensures that you make the most of the available space in your bag.
Another factor to consider is the time and effort required to use a stuff sack. Compressing a sleeping bag into a small stuff sack can be a time-consuming task, and it may not always be worth the extra effort. If you're car camping, for example, compressing your sleeping bag to a very small size may not be necessary, and a regular stuff sack or even just a large bag for transportation and storage might be more practical.
Additionally, it's worth noting that leaving a sleeping bag in a compressed state inside a stuff sack for extended periods can negatively impact its lofting ability and resilience. Both down and synthetic bag insulations have limits to their resilience, and prolonged compression can compromise their performance. Therefore, it is generally recommended to store sleeping bags in a loose, breathable cotton or mesh sack to maintain their condition.
In conclusion, while a stuff sack can be useful in certain situations, it is not always necessary. Depending on your specific needs and constraints, alternative methods like using trash compactor bags, larger sacks, or no sack at all, might be more suitable. The key is to find the approach that best suits your activity, optimises space, and maintains the condition of your sleeping bag.
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Frequently asked questions
There are a few ways to determine the volume of your sleeping bag in litres. Firstly, you can measure the bottom diameter of the bag, find the circle area and multiply that by the height to get the approximate volume. Alternatively, you can stuff your bag into something like a bucket and then measure the volume of the used part of the bucket. You can also use the cylinder volume calculation formula and convert the result from cubic centimetres to litres.
It depends on whether you're backpacking or car camping. If you're backpacking, you'll want to compress your sleeping bag as small as possible to save space in your backpack, so a compression sack is recommended. If you're car camping, a regular stuff sack will do.
The type of stuff sack you need depends on the size, shape, and fill of your sleeping bag. Down sleeping bags are more compressible and require lower volume stuff sacks, while synthetic-filled sleeping bags need higher volume stuff sacks.
A rule of thumb is to take the compressed volume of your sleeping bag and add 5 litres. For example, if your sleeping bag has a compressed volume of 5.3 litres, you'll need a compression sack of at least 10.3 litres.
