What Size Backpack Do You Need for a Day Hike?

That said, the "right" size depends on several factors: how long you will be out, the season, the weather forecast, and whether you are carrying gear for other people. A two-hour summer stroll on a well-marked trail needs far less capacity than a full-day winter ridge hike where you are packing extra layers, traction devices, and a thermos of hot soup.

The rest of this guide breaks down exactly what size you need for every scenario, what should go inside, and which features matter more than raw liter count. If you already know your size and just want pack recommendations, jump to our best hiking backpacks roundup.

Backpack capacity is measured in liters (or sometimes cubic inches in the US). One liter equals roughly 61 cubic inches. The number tells you the total internal volume of the main compartment plus any included pockets. A 20-liter pack, for example, holds 20 liters of stuff — about the same volume as a standard office water cooler jug.

Liters are not the whole story. Two packs rated at 22 liters can feel dramatically different depending on their shape, pocket layout, and compression system. A tall, narrow pack distributes weight differently than a short, wide one. External attachment points — daisy chains, bungee cords, ice axe loops — effectively add capacity without increasing the liter count. When comparing packs, think of liters as a starting point, not the final answer.

Packing volume vs. stated volume. Manufacturers measure volume by filling the pack with small plastic balls and measuring displacement. In real life, your gear does not pack as efficiently as tiny balls. A bulky fleece jacket might take up 5 liters of space even though it compresses down to 2 liters in a stuff sack. Plan for about 70-80% packing efficiency — meaning a 20-liter pack realistically holds about 14 to 16 liters of loosely packed gear.

For a deeper dive into how pack volume relates to torso length and hip belt sizing, see our how to choose backpack size guide.

Your pack size should be driven by what goes inside it, not the other way around. Here is a realistic breakdown of day hike essentials and the approximate volume each one takes. For the complete list, see our day hike packing list.

There are specific scenarios where you should go larger than the standard 20-25L day pack. If any of these apply to you, consider jumping to the 25-35L range.

Winter hiking. Cold-weather gear is bulkier across the board. A puffy jacket takes twice the space of a wind shell. Add microspikes or snowshoes strapped to the outside, insulated gloves, a balaclava, a thermos, and hand warmers, and you can easily fill 30 liters. Our hiking layering system guide explains how to layer efficiently so you carry fewer but smarter pieces.

Photography gear. A mirrorless camera body with one lens adds about 3 liters of volume and a full pound of weight. If you carry a second lens, filters, or a small tripod, you need a pack that can accommodate a padded camera insert or at least has enough room to wrap the camera in a fleece for protection. Check our hiking photography tips for more on how to carry camera gear comfortably.

Carrying gear for kids. If you are hiking with young children, you are the pack mule. Their water, snacks, spare clothes, diapers, sunscreen, and toys all go in your pack. A 30-35L pack gives you the space without forcing you into a full-frame backpacking pack.

Extended day hikes (8+ hours). Long days in the mountains mean more food, more water, and more contingency gear. If you are out for dawn-to-dusk on a big summit push, you will appreciate the extra capacity of a 28-32L pack.

Bigger is not always better. In these scenarios, a smaller pack actively improves your experience:

Trail running. Running vests and race packs in the 5-12L range are purpose-built for speed. They sit tight against your body, minimize bounce, and carry just enough for water, nutrition, and a wind layer. If you are running trails rather than hiking them, a standard day pack will bounce and chafe.

Short loops and nature walks. For a two-hour loop on a well-maintained trail close to the car, a 10-15L pack — or even a hip pack or sling bag — is plenty. You need water, a snack, sunscreen, and your phone. Carrying a 25L pack half-empty just adds unnecessary weight and bulk.

Ultralight approach. Dedicated ultralight hikers are intentional about every gram. If you have dialed in your kit with lightweight rain gear, a compact first aid kit, and bars instead of a full lunch, you can often fit a full-day load into 15-18 liters. See our ultralight backpacking guide for strategies that apply to day hiking too.

We have tested dozens of day packs over thousands of trail miles. Rather than duplicate our full reviews here, we will point you to the right roundup based on your needs: