I am confused about the capacity figures that backpack manufacturers claim. With particular regards to daypacks it seems that the figures advertised are always about 20% higher than what the pack actually holds. What gives? And how many cubic inches do I need for a daypack or a week-long pack?Submitted by - Jeane, Fort Collins, CO
You are not alone in your confusion. We often test packs that claim the exact same capacity, but find that one holds much more gear than the other. It is somewhat baffling—especially because the measuring process has been standardized for several years.
The standard entails using 20mm plastic balls as the filler. Packs are loaded up, then emptied and then contents are dumped into measuring devices. According to the standard, capacity measurements should not include any compartments that are not entirely sealed by zippers—such as shovel pockets, bottle holders, compression pockets, etc. But I suspect that some of the overstated daypack figures you mention erroneously include the capacity of these pockets. It can be very deceiving and frustrating, especially if you’re shopping online and don’t have the ability to compare sizes in person.
Another point of confusion is that some packs are measured in cubic inches and some are measured in liters. Most companies are stating capacities in liters these days, but not everyone. In general, a daypack will be under 2,500 cubic inches or 40 liters. Weekend packs are typically 2,500 to 4,000 cubic inches or 40 to 65 liters. Weeklong packs range from 4,000 to 6,000 cubic inches or 65 to 95 liters. And expedition packs are 6,000 cubic inches or 95 liters and up.
The most foolproof way to be sure that you’re getting the size you need is to compare in person. Bring your typical dayhiking load to the store with you to make sure it fits. But if you’re shopping online, it pays to ask questions. Make some phone calls (to the manufacturer, not the online retailer) and pry. It just might save you 15 bucks in return shipping. —Kristin