How to Choose a Backpack Size for Hiking
Backpack size is measured in liters, and the right size depends entirely on trip length, not how much stuff you want to bring. Oversizing leads to overpacking, which leads to a heavier, more uncomfortable hike.
Size by Trip Length
| Trip Type | Recommended Size | What Fits |
|---|---|---|
| Day hike | 15-25L | Water, snacks, layer, first aid, basics |
| Overnight (1 night) | 30-45L | Sleep system, food, shelter, clothing |
| Weekend (2-3 nights) | 45-60L | Above plus more food, fuel, extra layers |
| Extended (4+ nights) | 60-75L+ | Multi-day food, full shelter system, extra gear |
Factors That Push You to a Larger Size
Cold weather trips require bulkier insulation layers and a heavier sleeping bag, which eat up space fast even on short trips. A 3-season overnight might need a 35L pack, while the same trip in winter could need 45L or more for the same gear list.
Carrying gear for others, like kids’ supplies or shared group equipment (tent, stove), adds volume that doesn’t show up in your personal gear list.
Photography or specialized equipment takes up dedicated space that a minimalist packing list doesn’t account for.
Factors That Let You Go Smaller
Lightweight or ultralight gear (quilts instead of sleeping bags, tarps instead of tents) can shave 20-30% off the volume needed for the same trip length. If you’ve already invested in lighter gear, don’t default to the size chart above without adjusting down.
Fit Matters as Much as Size
A pack that’s the right liter count but doesn’t fit your torso length will be uncomfortable regardless of capacity. Measure your torso from the C7 vertebra (the bony bump at the base of your neck) to the top of your hip bones, and match that to the pack’s torso size range, usually listed in inches on the product page.
Test Loaded, Not Empty
An empty pack always feels comfortable. Load it with the weight you’d actually carry (or close to it) before deciding on fit, since hip belts and shoulder straps behave differently under load.
When in Doubt, Size Down
A pack that’s slightly too small forces better packing discipline. A pack that’s too big invites overpacking, which means more weight on your back for no reason. If you’re between two sizes, the smaller one is usually the better long-term choice.
FAQ
What size backpack do I need for a 3-day hike?
A 45-60L pack typically covers a 2-3 night trip with standard (non-ultralight) gear in moderate conditions.
Does backpack size include capacity for water?
Yes, water reservoir space is part of the total liter count, so factor in 2-3L of water capacity within your overall size choice.
Can I use a larger backpack for day hikes?
You can, but a pack much larger than needed tends to shift and bounce since it’s not loaded enough to fill out properly, and it adds unnecessary weight.
How much does torso length matter compared to liter capacity?
Torso length matters more for comfort. A correctly sized pack with the wrong torso fit will cause shoulder and hip pain regardless of how well the capacity matches your gear list.
