Because sleeping bags vary in their packed volume (depending on whether they are down or synthetic and as a result of different shell/liner fabrics), it's not possible to simply equate a bag temperature rating with a compression sack size.
The best way to determine if your bag will fit in a specific compression sack is to measure its moderately compressed volume. Here's how:
- Put your bag in a cardboard box (one which is larger than the bag)
- Measure the length and width of the box in inches
- Press the sleeping bag down firmly until the upper surface is roughly level in the box
- Measure the average depth that the bag occupies in inches
- Now multiply length x width x depth = volume in cubic inches
- Divide the total by 61 = volume in liters
You'll find the volume of our compression sacks in liters on the product pages
If you need compression and waterproof protection and weight is not critical, we'd suggest the eVent Compression Dry Sack. The eVent Compression Sack - Size M compresses from 14 down to 4.5 liters; weight is 5.2 ounces.
If you need compression and waterproof protection, and weight is critical, we’d suggest the UltraSil Compression Dry Sack with eVent. UltraSil Compression Dry Sack with eVent – Size M compresses from 14 down to 4.5 liters; weight is 3.2 ounces.
If you need compression but not waterproof protection and weight is critical, we'd suggest the Ultra-Sil Compression Sack. Ultra-Sil Compression Sack - Size M compresses from 15 down to 5 liters; weight is 3 ounces.
One other thought about storage for sleeping bags and insulated jackets:
If you need waterproof protection but do not need maximum compression, we'd suggest the eVac Dry Sack. The eVac Dry Sack - Size 13 Liter weighs 2.4 ounces. Note: When you pack your soft goods in the eVac sack, roll and click the roll-top closure then sit on the bag to squeeze out air through the eVent fabric base. Roll the roll-top closure down tighter and you've achieved a reasonable degree of compression. You'll need to pack the bag into your backpack and pack other gear on top to prevent it drawing air back into the eVac sack.