If you have purchased a Sea to Summit sleeping bag, you can find the volume of the bag on our product pages. If your sleeping bag is from another brand, you can usually find the size of the stuff sack supplied with the bag on the manufacturer's website or on the product specifications page of a retailer's website. The capacity of the stuff sack is usually equal to the mildly compressed volume of the sleeping bag.
If you don't have the stuff sack, you can determine the volume of your sleeping bag by following these steps:
Put your bag in a cardboard box that 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 (the bag is now mildly compressed).
Measure the average depth that the bag occupies in inches.
Multiply length x width x depth = volume in cubic inches.
Divide the total by 61 = volume in liters.
Alternatively, you can measure in centimeters and divide the total by 1000 to calculate the volume in liters.