What size backpack do you need? Guide to 20L, 30L, and 40L sizes (Day vs. Weekend)

Why volume is your best ally (or your worst enemy)

Choosing the right size hiking backpack is a much more strategic decision than it seems. A pack that's too small forces you to leave essentials at home (water, jacket, food), while a pack that's too big quickly becomes an unnecessary burden that tires your back and slows you down.
At Monsacparis , we know that a well-sized bag completely transforms the outdoor experience. Whether you're heading out for a day hike, a sporting walk, or a weekend trek, understanding the difference between a 20L, 30L, or 40L bag is the key to walking longer, more comfortably, and with more enjoyment.

I. Understanding “Litrage”: what does it really mean?

The capacity of a hiking backpack refers to its total internal volume , expressed in liters. A 30-liter backpack can theoretically hold 30 liters of equipment.

⚠️ The trap to avoid

Two 30L bags can look very different once they are carried:

• Number and size of exterior pockets

• Presence of separate compartments

• Back structure (rigid or flexible)

👉 Result: a “poorly organized” bag appears smaller than a well-thought-out bag.

🎒 Expert advice from Monsacparis

The larger the volume, the more essential the carrying system becomes:

• Ergonomic shoulder straps

• Breathable back

• Waist belt (essential for sizes 30–40L and above)

A good bag distributes the weight across the hips, not just the shoulders.

II. The 20L Hiking Backpack: Essential for Day Hikes

For whom?

• Occasional hiker

• Quick outings (2 to 5 hours)

• Speed ​​hiking , power walking, light trail running

What can you put in a 20L bag?

• Water bladder or water bottle (1.5 to 2L)

• Windproof or waterproof jacket

• Light picnic / energy bars

• Phone, keys, wallet

• Mini first aid kit

Benefits

• Ultra-light

• Excellent freedom of movement

• Ideal for technical terrain

Boundaries

• Not well suited to winter

• Not enough room for extra clothes

👉 At Monsacparis , our 20L bags prioritize breathability , lightness and compactness.

III. The 30L Hiking Backpack: Absolute Versatility

For whom?

• Regular hikers

• Full-day outings

• Hiking in all seasons

• Outings with children

What you can put in a 30L bag

• The entire contents of the 20L

• Fleece or lightweight down jacket

• Rain jacket + overtrousers

• Complete first aid kit

• Camera / binoculars

• A more substantial picnic

• Trekking poles (external attachment)

Why is the 30L bag the most popular?

• It covers 80% of uses

• Compact enough, yet very versatile

• Excellent balance between comfort and capacity

💡 Monsacparis Advice
If you're hesitating between 20L or 30L for your first purchase: choose 30L . You'll always have some leeway.

IV. The 40L+ Hiking Backpack: for Weekends and Adventures

For whom?

• 2-day hike

• Night in a guesthouse, mountain refuge or light bivouac

• Beginner trekking

• Adventure trip + hiking

What can you put in a 40L bag?

• Change of clothes

• Compact sleeping bag

• Sleeping bag sheet

• Toiletry bag

• Lightweight stove

• Food for 2 days

• Headlamp, external battery

The key purchasing criterion

👉 A padded waist belt is mandatory
It allows you to:

• Transfer 60–70% of the weight to the hips

• Reduce shoulder fatigue

• Walk longer without pain

🎒 MonSacParis 40L bags are designed for:

• A stable carrier

• Enhanced ventilation

• Smart compartments

Ready for adventure? Explore our backpacks designed for trekking and nature weekends.

V. Summary Table: What volume for what use?

VI. 3 Essential Criteria Beyond Volume

1️⃣ Morphology

• Height-adjustable back

• Women's specific models (shorter straps, adapted shape)

• Adjustable belt

2️⃣ Accessorizing

• Integrated rain cover

• Stick holder

• Safety whistle

• Compatible water bladder

3️⃣ Ventilation

• Mesh back or open-cell foam

• Reduction of perspiration

• Increased comfort in summer

👉 At Monsacparis , each bag is selected for its balance between comfort, durability and understated design , usable both in nature and while traveling.

Ready to take the start?

Choosing the right size hiking backpack is an investment in your comfort and enjoyment.
👉 The 20L for lightness, the 30L for versatility, the 40L for adventure.
If you are a beginner, the 30L remains the safest choice .

Don't let an unsuitable bag ruin your outing. Discover our Monsacparis collection of hiking bags now and find the perfect companion for your next adventures.

FAQ – Frequently Asked Questions

What size backpack is needed for a day hike?

👉 Between 20L and 30L , depending on the season and your equipment.

Can a 40L hiking backpack be used as cabin baggage?

👉 Yes, most 40L bags comply with cabin dimensions, provided they are not overfilled .

How to adjust your hiking backpack to avoid back pain?

👉 Start by tightening the waist belt , then adjust the shoulder straps. The weight should rest on your hips, not your shoulders.