Daypack Size Guide: 15L vs 20L vs 27L vs 38L Backpacks

Backpack capacity is easiest to understand when you start with the gear you actually need to carry. A smaller number does not automatically mean a better daypack, and a larger number does not automatically mean more comfort. The right size depends on trip length, weather, water, layers, food, emergency items and how bulky your gear is.

This guide compares common small and medium backpack sizes without assuming that one capacity works for every person or route.

Quick capacity comparison

15L: compact essentials

A 15L pack suits a short gear list: water, a light layer, snacks, phone, keys and a few personal items. It can work well for brief walks, sightseeing and everyday carry when you want a compact packed shape.

18L: flexible light carry

An 18L pack provides a little more room for an extra layer, food or travel items while remaining compact. Packable designs are especially useful as a secondary bag, but they may organize and support a load differently from a structured hiking pack.

20L: classic day-hike range

A 20L pack is a practical starting point for many day hikes. It can accommodate water, food, weather layers and a basic safety kit if those items are reasonably compact. Cycling and hydration-oriented designs may divide this capacity among several smaller pockets.

27L: longer days and changing conditions

A 27L pack adds room for bulkier clothing, more food, extra water or shared items. It can be helpful when weather changes during the day, but the larger volume should still match your torso and load.

38L: extended or bulky day loads

A 38L pack moves toward overnight or equipment-heavy use. It may suit a long day with bulky layers or a light overnight list, depending on the gear. At this size, load transfer, shoulder adjustment and packing balance matter more.

Start with a gear list, not the capacity label

Lay out your essentials before comparing packs. Include water, food, rain protection, insulation, navigation, first-aid items, power, personal items and any activity-specific equipment. Add the least compressible items first. If the list barely fits, choose the next size or reduce the load instead of overstuffing the bag.

Capacity is not the same as fit

Two packs with the same liter rating can feel very different. Compare torso position, shoulder-strap shape, sternum-strap adjustment, back-panel contact and how the load sits when you move. A compact pack that fits well can be more comfortable than a larger pack with poor load placement.

Check organization and access

Consider how you will reach water, a rain layer, snacks and small essentials. A single main compartment maximizes flexible space, while several pockets make small items easier to find. External stretch pockets and hydration routing can also affect how much of the stated capacity remains available inside.

Packability versus structure

Packable backpacks fold into a small stored format and work well as travel or backup bags. Structured hiking packs usually hold their shape and manage heavier loads more effectively. Choose based on the load you expect rather than weight or packed size alone.

Weather and care

If rain is possible, check whether the pack includes a cover or whether sensitive items need waterproof inner bags. After use, empty every pocket, remove loose dirt and let the pack dry fully before storage. Follow the product care instructions rather than assuming every fabric can be machine washed.

Compare BLACKPONGO backpack options

• RillCore A54 15L Packable Backpack for compact carry.
• Cloudwing 18L Packable Backpack for light travel and secondary-bag use.
• TrailFlow 20L Cycling and Hiking Backpack for an organized day load.
• VaneCore Dragonfly 27L Packable Backpack when you need more flexible space.
• PeakCore 38L Hiking Backpack for larger or longer-trip loads.

Browse all BLACKPONGO backpacks, or continue with our complete hiking backpack guide for fit, adjustment and access details.