What size daypack do I need for hiking?

For most day hikes, 20-25L is the sweet spot: enough room for layers, lunch, 2L of water, and the ten essentials without inviting overpacking. If you carry camera gear, hike in cold weather where you need bulkier layers, or do long all-day routes, step up to 28-35L. Sub-20L packs work for short, summer-weather trails where you mostly need water and a snack.