best 75L rucksack in india

How To Calculate Litre Capacity of a Bag? How Big is Your Backpack?

Whether you are a frequent traveller or an adventurist, one of the essential companions you need to carry with you is the Rucksack bag. When it comes to a backpack or rucksack bag, it should be able to handle everything you would need for surviving for the period that you would be on the move.

From that perspective, it is essential to understand how much capacity does your new bag offer, or rather how to calculate litre capacity of a bag. Let us check out the options you can use to measure the capacity of a rucksack bag. In addition, we will also check out a few specific sizes of the bags and learn how they fulfil your needs.

How to Calculate litre capacity of a bag?

Well, ideally you will find it described on the bag. However, if you are unsure of the volume capacity of your bag or just looking to confirm the claims of the manufacturer, there are a few options and methods you can use to calculate litre capacity of a bag.

One of the common methods used is to use small Ping-Pong balls or dried beans to find the volume of your bag.  Prepare a few balls or collect enough dried beans and begin the exercise.

  • Take a measuring cup and begin filling your bag with the beans or balls.
  • Once the bag is full, you are aware of the number of the cups you needed to fill the bag to its full capacity.
  • Based on the measuring cup size and the number of cups used, you can easily arrive at the litre capacity of your bag.

For instance, if the measuring cup is of 500 ml capacity and you have used 40 cups, the total capacity of the bag is 20 litres. While you may fill the main compartment alone or fill out the outer pockets as well.

How big is a 20 litre backpack?

The 20-litre backpack capacity should be ideal for daily travels. In case your travel begins in the morning and ends by night, it should be an ideal option for your needs. The size is quite limiting, and you will need to go through a lot of compromises, but being precise, how big is a 20-litre backpack?

A 20-litre bag should meet the following needs:

  • The bag is ideal for a day’s travel, definitely not more than that.
  • Filled to the fullest capacity, it should ideally have a weight of around 7 to 9 kgs depending on the material used.
  • The weight of the empty bag measures around 800 to 900 grams.
  • The bag should ideally take a load of a good sleeping mat, a pair of trousers, a bottle, along with a jacket and a pillow.

How big is a 25 litre backpack?

A 25-litre backpack is ideally a good option for you – once again a daily trip. If your needs are slightly more than what we have outlined above, a 25-litre bag can be a good option. In a way, there should not be a huge difference between a 20 litre and 25-litre bag.

But how big is a 25-litre backpack? The 25L backpack should ideally meet the below needs:

  • Best suited for a day’s travel. The maximum it can take is an overnight stay.
  • The bag should pack an additional pair of clothes than what we specified above. The bag should be able to host your laptop as well.
  • The full filled bag should weigh around 10 kg.
  • The empty bag weighs around 900 grams to a kg.

How big is a 30 litre backpack?

The 30-litre bag can be a perfect match for those looking for the weekend trips that may take around three days max. It will let you carry sufficient options for survival through a couple of days.

But how big is a 30-litre backpack? Ideally, you could expect the below from a 30-litre Rucksack bag:

  • In addition to your daily wear, water bottles, and other items we already covered above, the bag should let you carry a sleeping bag as well. You should be able to carry spare clothing, water, food, and other essential items.
  • The empty bag should weight anywhere between 600 grams to 1000 grams depending on the material and design.
  • Filled to full capacity, it should weigh around 12 to 13 kgs.
  • The bag is best suited for use on the weekend trips. You may need to make a choice between sleeping bags and other essentials.

How big is a 40 litre backpack?

The 40-litre backpack comes under the medium rucksack bags. It should be your ideal companion for overnight camps, hiking and similar other requirements. They can carry heavier loads than the day packs we just discussed.

Again, but how big is a 40-litre backpack? A few features that these 40L bags come with include:

  • The bag should weigh around 1 kg to 1200 grams when empty.
  • The fully filled weight of the bag will range between 12 to 15 kgs.
  • The bags come with all the features on a 30-litre bag but will pack in extra options for additional padding and storage. Camping gear or sleeping bags or a couple of additional utensils should ideally be accommodated.
  • The 40 litre backpack is an excellent option for overnight camps and other high demand needs.

50 vs 65-litre backpack – How to Choose?

Are you confused between a 50 litre vs 65-litre backpack? Well, it should be dependent upon what you tend to carry. A 50-litre bag should ideally weigh at 13 to 15 kg, while the 65 kg bag should weigh around 18 to 20 Kgs.

Carrying weight worth 20 kgs may not be an ideal condition. Of course, when you have a larger bag, you tend to be tempted to carry more. We would want to stick with a capacity of around 50 kgs as such, and we believe it can help you carry enough of the needs. Of course, if you are with a family, you will need more items to carry and be forced to opt for a larger bag. Even then we would advise opting for a 50 kg bag itself, or better still two bags with 50 kg and 20 kg so that you can share the weight between your family members.

65 vs 75-litre backpack

This is yet another confusion that frequent travellers tend to face quite regularly. We would indeed not recommend opting for a bag with a high capacity as 75 litres. Of course, a bigger bag is tempting, and you would feel like carrying your entire wardrobe! But is it really needed?

What is most important is the personal packing style. Keep yourself confined to the exact requirements. With high capacity bags like 75 litres, you may tend to break your back. Moreover, with that kind of a load on your back, you would not be able to enjoy your trip either.

Which Backpack is Right for me?

Now that we have understood how to calculate litre capacity of a bag, how big is a 30-litre backpack, 40-litre backpack etc… now let’s see which is the right backpack for you. Here is a small infographic which shall help you to understand which backpack size should be the best pick for you.

how to calculate litre capacity of a bag

The Parting Thoughts on Litre Capacity of a Backpack

With the above, you should now be familiar how big is a 25/30 etc… litre backpack and how to calculate litre capacity of a bag. The crux of the matter is to learn to pack your bags with a proper focus on the right things that you will be using in your trip.

Please share your thought below on how much can you fill-in in your backpacks, in the comment section below.


  1. Ping pong balls? Just measure the bag in cm’s and multiply HxWxD. 100 cubic cm = 1 litre.
    Pillow in a 20 litre bag,? it must be blow up. 7 to 9 kilos in 20 litre bag? Must have a couple of bricks in it.

    1. Hi Anthony Dunne,
      We do appreciate your deeper knowledge on the topic under discussion. Kindly note that the post here is for those who do not understand the technical aspects. The conversion between cubic cm and litre may not be easily understood by those people. The method of ping pong balls would be more of a good option for them for arriving at the right calculation.
      As for your second query, the weight carried by the bag would be dependent on the material used for the bag. The calculation is based on the volume of the bag and not the carrying capacity of the person using the bag.
      We would request you to kindly share the tips in a more friendly way so that our readers can benefit. Sharing your knowledge would be a better option than being sarcastic.

    2. *1000 cubic cm = 1 litre

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