For those of us who spend a lot of time in our hiking boots and absolutely loathe rolling up a sleeping bag, the camping gear gods have managed to manufacture a neat little tool known as the compression sack. A compression sack does just that, compresses large sleeping bags down to something manageable.

When it comes to what size compression sack for a sleeping bag you need, you simply need to know the dimensions of your sleeping bag. Or, you can base it on the size of the holding bag that came with your sleeping bag. Also, depending on the manufacturer, you may need to convert English to metric or vice versa.

Some manufacturers only use metric specifications or the other way around. If you’re skimming Amazon, you may come across liters and centimeters and find one in gallons or inches on the very next screen.

It pays to have a little brand bias when it comes to sleeping bags and related gear. If you stick to the same brand, you can more easily keep track of what the sizes are and aren’t, along with what gear you like and the gear you don’t.

I’ve written another article on how to properly roll up a sleeping bag.

How to figure out what size compression sack you need

In this article, we’re going to dive into two ways of finding out which size compression sack you need for your sleeping bag:

  1. Using your stuff sack as a reference
  2. Looking at the dimensions of your sleeping bag

Let’s dive straight into method #1, shall we?

1. Using your stuff sack as a reference

The methodology behind this measurement is as simple as it gets. You stuff your sleeping bag down into the stuffing sack that came with it, then purchase a compression sack that is ever so slightly larger.

It’s almost a foolproof option. Of course, not every sleeping bag comes with its own stuff sack, even though they should. However, if you fall in the category of the vast majority of sleeping bag purchasers who get stuffing sacks with their bag, then you have a pretty easy method for picking out the right size compression sack.

The goal is to get that jumbo, luxury sleeping bag you bought jammed down into the tightest dimension that it can reach so that you can tackle that 10-mile hike tomorrow morning without your sleeping bag billowing out behind you like a jumbo flag.

In fact, you can take it a step further by using a vacuum cleaner with a hose attachment. The goal is not to vacuum seal the sleeping bag in your compression sack, but to suck out all of the available air pockets still remaining in both the sleeping bag and the compression sack.

Here’s how to use the vacuum cleaner and the compression sack:

  • Fold your sleeping bag by laying it flat on the ground and folding it directly in half
  • Use your hands to press all of the air out of the sleeping bag
  • Fold it lengthwise a second time
  • Use your hands to press all of the air out
  • Fold it widthwise and use your hands to press the air out
  • Now stuff it into the compression sack
  • Cinch the compression sack closed
  • Attach a vacuum hose to your vacuum
  • Insert the end of the hose into the compression sack opening
  • Grab the material around the hose and squeeze down to create the best seal that you can
  • Turn on the vacuum
  • When the bag is compressed as far as it will go, turn the vacuum off
  • Immediately cinch it tighter and allow it to relax

Now obviously, there is still an opening, so air will get back into the bag, however, you’ve effectively compressed the bag as far as it will go, and even though some air will get back into the bag, it won’t return to the same size as it was when you crammed everything in there and hand-pressed the air out of the sleeping bag.

2. Looking at the dimensions of your sleeping bag

Another great method for determining the right size compression sack for your sleeping bag is to use cardboard and some math. Nobody likes math but unless you want to try and philosophize your way into the right-size compression sack, you’re going to have to suck it up and do some math, geometry style.

In this case, you’ll be determining volume, since most compression pack sizes are measured in volume, such as liters or gallons. The formula for getting the volume of a cube is length x width x height.

Of course, you have to have a cube to get that measurement of volume, and a sleeping bag is far from a cube. What you want is to get a box that you can stuff your sleeping bag intowithout having to strain so hard that you pop all of the capillaries around your eyes and pop a vein in your forehead.

Get your bag stuffed into the cardboard box to ensure that it fits without bothering to take a measurement. If you can stuff it in there relatively easily, go ahead and crush the box down to the point where it is flush with the sleeping bag within.

Get your length, width, and depth measurements and multiply everything out. That’s going to give you the answer in cubic inches and, of course, you need to convert that to liters. Don’t worry, you won’t need to look up one of Einstein’s equations; you simply have to divide the result by 61.

So, if your box measures 17”L x 20”W x 10”H, then you will come up with 3,400in³. Now, divide that number by 61 and you will get 55.74 liters, which is rounded up. That’s it. Now that you know the rough volume of your representative container, you can go shopping for the proper size compressions sack.

Will a compression sack damage your sleeping bag?

The Photographers Backpack
Photo by Alexander Andrews / Unsplash

As in everything – or, at least that’s the way it seems nowadays – there is a fierce divide over whether it is best to use a compression sack or simply roll up your sleeping bag. Now, there’s no denying the fact that even at its most compressed, you have what is essentially a large ball on a drawstring that you have to find space for.

However, that’s neither here nor there. The question is, does it damage your sleeping bag? The answer is no, it’s not going to damage your sleeping bag. Sure, it affects the loft of your bag because you’re compressing all of that material down as far as it will go.

Fortunately, that’s only a temporary thing, as it will return to form and “bounce back,” so to speak, as soon as you pull it out of your compression sack and shake it out.

What damages your sleeping bag is storing it in your compression sack for insanely long periods. Compressing the material that makes your sleeping bag a soft, comfortable, and well-insulated sleeping container is one thing. Doing so for months on end is entirely different.

At some point, in other words, you won’t get a “bounce back” when you fluff the sleeping bag out after being in your compression sack for six months to a year.

Types of compression sacks

There are basically three types of compression sacks available on the market:

  • Webbing strap compression sacks
  • Fold over compressions sacks
  • Waterproof compressions sacks

The webbing strap variety of compression sacks are just like they sound. After you are finished compressing your sleeping bag within the sack, you have a series of webbing straps that go over the top and cinch the bag shut.

The fold-over compression sacks fold over the top as you finish compressing the bag. This is also known as a “roll-top” design but it essentially boils down to the same thing. Whether you want to term a top that rolls over the opening, rather than folds over, is entirely up to you.

Last but not least is the waterproof variety, which can encompass either of the above two. While the first two are going to have waterproof features, the waterproof compression sacks focus their designs more on keeping water out.

Difference between a stuffing bag and a compression sack

There is no difference between the two. A stuffing sack and a compression sack are really the same, exact thing. However, there is a key difference. The stuffing bag is basically a bag that holds your sleeping bag whenever you are traveling or packing up camp for the end of the weekend.

The compression bag is the same thing, only it is designed to be the smallest sized bag that is possible for your sleeping bag to still smash down into it. It’s your stuffing bag in miniature. That’s also why it’s important to know your compression bag sizes, as discussed above, so you can pick the right size.

If your compression bag allows for some elbow room after you stuff your sleeping bag down into it, then you are really carrying around a stuffing sack/bag and you should probably go a little smaller.

Final thoughts

Determining your compression bag size isn’t incredibly difficult as there are a couple of ways to do it. If you’re a veteran camper/hiker, then you probably have a pretty good idea without doing any kind of measurement at all.

Most of the time, you don’t have to measure anything anyway, as many compression sacks will reflect your sleeping bag’s material and dimensions. Whether you decide to smash a cardboard box or just look up the dimensions, you’ll find the right compression sack for you.