For most long day hikes, a backpack between 20 and 30 liters is the sweet spot. It provides enough room for food, water, extra layers, and safety essentials without becoming unnecessarily heavy.
I remember taking a much-too-large backpack on one of my first full-day hikes. Because I had the extra space, I naturally filled it—with spare clothes, too much food, and plenty of things I never actually used. By the end of the day, my shoulders definitely noticed. Once I switched to a smaller daypack, I became much more thoughtful about what I carried, and hiking immediately felt more comfortable.
The best backpack isn't necessarily the biggest one. It's the one that comfortably carries everything you genuinely need.
The Short Answer
For a long day hike, a 20–30 liter backpack is usually ideal.
As a general guide:
-
10–20L: Short or minimalist day hikes
-
20–30L: Most long day hikes
-
30–40L: Cold weather, technical hikes, or trips requiring additional equipment
-
40L+: Usually better suited to overnight or multi-day backpacking
Your ideal size will depend on the weather, distance, and amount of equipment you need.
1. Why Is 20–30 Liters a Good Size?
This range provides enough room for the essentials without encouraging you to overpack.
You can usually fit:
-
Water
-
Lunch and snacks
-
Extra clothing
-
A waterproof jacket
-
First aid supplies
-
Navigation equipment
-
Sun protection
-
Emergency essentials
For most full-day adventures, that's plenty of space.
2. Consider the Weather
Weather can significantly affect how much space you need.
A summer hike may require only a lightweight layer and rain protection, while colder conditions could mean packing:
-
A fleece
-
An insulated jacket
-
Gloves
-
A warm hat
In colder weather, a backpack closer to 30 liters may be more practical.
3. Think About How Much Water You'll Carry
Water can take up a surprising amount of space and weight.
If there are no reliable water sources along your route, you may need to carry several liters.
Look for a backpack with:
-
Side bottle pockets
-
Hydration reservoir compatibility
-
Easy access to your water
Being able to drink without unpacking your bag is especially useful on longer hikes.
4. Fit Matters More Than Capacity
A 25-liter backpack that fits properly will usually feel much better than a 20-liter pack that doesn't.
Look for:
-
Comfortable shoulder straps
-
A supportive hip belt
-
An adjustable chest strap
-
Good weight distribution
Your backpack should sit close to your body without restricting your movement.
5. Don't Choose a Bigger Pack "Just in Case"
Extra space makes it surprisingly tempting to bring unnecessary items.
A larger backpack can lead to:
-
Overpacking
-
Extra weight
-
Shoulder discomfort
-
Faster fatigue
Choose enough capacity for your actual needs rather than planning for every possible scenario.
What About an Overnight Hike?
For an overnight trip, you'll normally need more capacity because you're adding a shelter, sleeping equipment, and additional food.
Many backpackers use packs around 40–60 liters for overnight and multi-day trips, although the exact size depends heavily on how compact their equipment is.
A Quick Aside About Backpack Weight
One thing I've learned is that backpack size matters less than what you put inside it. Even a small daypack can become uncomfortable if it's overloaded. Pack the essentials first, remove unnecessary duplicates, and keep heavier items close to your back. A thoughtfully packed backpack almost always feels better than a larger one filled with "just in case" gear.
My Personal Takeaway
For most long day hikes, a 20–30 liter backpack offers the best balance between space and comfort. It gives you enough room for water, food, clothing, and safety essentials without tempting you to carry too much. More importantly, choose a backpack that fits your body comfortably—because after several hours on the trail, good fit matters far more than a few extra liters of storage.