Thanks for reaching out! Generally, when talking about a compression sack or stuff sack and a company only gives you two measurements, it is because the sack is a cylinder. The first measurement is the diameter of the bottom of the sack and the second is the length/height. As such, with the measurements of 23X38 cm, that would give you a volume of 15788 cubic cm, or 15.78 liters. At that volume, we would recommend going with a 20 liter compression sack, like the REI Co-op Lightweight Compression Stuff Sack or the Sea to Summit Ultra Sil Compression Sack. The extra room will make it easier to get the sleeping bag into the sack before you compress it down.

Hopefully this helps, thanks!

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