Sea to Summit eVent Compression Sack

This question was asked by
Stafford Lightman

I have a 3-4 season good quality down sleeping bag (Western mountaineering ultralight). what size SEA TO SUMMIT EVENT COMPRESSION SACK do I need?

The Western Mountaineering dimensions are 18 x 33cm so you would require a Small Compression Sack as the dimensions of this is 18 x 40cm.