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Designing for Total Size or Capacity

Travel Packs

A 65 litre Backpack in a Medium Harness Length

Daypack Capacity

If we determine that the daypack size is to be 20 litres - White Mountain Backpacks™ do not include the compressed portion of the daypack when zipped to the main body of the travel pack in stating the total pack capacity.  This would constitute approximately 33% to 50% of the daypack capacity, or 5 to 10 litres depending on the travel pack series or design choice. If we allow the compressed portion to be 10 litres or half the daypack capacity, this would leave a balance of 10 litres.  Please note, that some manufacturers do include the compressed portion of the daypack to represent the total pack capacity.

Main Body Capacity

We would then need to construct the main body of the travel pack to be 55 litres (daypack 10 litres plus the main body of the pack at 55 litres, for a total travel pack capacity of 65 litres).  The total length of the Internal staves would be a Medium Size Stave length of 60cm. We would then include 5cm of backpack outside the Stave Length, for total backpack length of 65cm.  With a total travel backpack length of 65cm and an acceptable approximate width of 35cm (keeping within the average body width), we would need a depth of approximately 24cm to ensure the main body of the travel pack was 55 litres.

The total Travel Pack size and capacity would then be;

Pack Length 65cm x Width 35cm x Depth 24cm = 54,600 cubic cm or 54.60 litres.
= Approximate total Travel Pack Capacity is 55 litres plus daypack of 20.00 litres
= Net Total Travel Pack Capacity of approximately 75 litres, or 70 litres when excluding the compressed portion of daypack when zip to the main pack body..

Hike Packs

A 65 litre Backpack in a Medium Harness Length


Hike packs do not have the extra capacity of a removal daypack as in the travel packs and would compensate for this loss of capacity, by having a top pocket in the lid and extra loading capacity above shoulder height. With hike packs we are not restricted in the length of the back pack, as hike packs are top loading and can extend past shoulder height. On some hike packs as in the White Mountain Backpacks™ Main Peak series, the lid of these backpacks can be extended to sit on top of the storm collar giving an extra 15 or more litres which is not stated in the hike pack capacity. It is important when designing hike packs to allow for head room in the design when proceeding past shoulder height, or as you would imagine the hike pack would be very uncomfortable to wear.

Top Lid Capacity

If we determine that the top lid is to be 5 litres and the hike pack 75cm in length, we would then proceed to construct a hike pack with a capacity of 60 litres.

Main Body Capacity

To construct a hike pack of 65 litres in a Medium Back Size, we would proceed as follows. The total length of the hike pack staves would be Medium Size Stave of 60cm, plus 5cm of backpack above the harness, or backpack length of 65cm. With a backpack length of 65cm plus the 10cm extension and an acceptable width of 35cm, we would need a depth of 23cm to establish a backpack capacity of approximately 60 litres.

The total Hike Pack size and capacity would then be

(Pack Length 65cm + Extended Length 10cm) x Width 35cm x Depth 23cm
= Gross Total Hike Pack Capacity of 60,375 cubic cm
= 60 litres plus Top Lid of 5.00 litres
= Net Total Hike Pack Capacity of 65.00 litres.

Further Considerations

It would not be wise to construct a 90 litre travel pack to fit an extra small back. The greater the backpack depth, the further the backpack is from the body, the further it is from the body, the more pressure is exerted on the lower back and chest through leverage. We would always endeavor to keep the backpack close to the body by limiting depth and construct all White Mountain Backpacks™ in a width no wider than the average body size. With Hike Packs, overall capacity can be increased by providing an extendable top lid, as in the Main Peak bushwalking pack, and the Antarctica hybrid travel pack. This feature allows the manufacturer to increase volume without affecting the rules applying to individual body size. This feature is not possible with the average travel pack.


Obviously these dimensions are variable, by determining a different depth or width to the above examples and the beginning or ending position of the internal staves the backpack shape can change dramatically. The above information is given as a broad example of the process in developing a backpack of a particular size to suit an individual back length. The above samples are an example of the calculations implemented in determining backpack capacity and vary greatly when backpacks are of a teardrop or tapered design. Some wholesalers and/or manufacturers also allow for expansion in their backpacks to determine the final backpack capacity. White Mountain Backpacks™ do not allow for expansion when calculating backpack capacity and it should be noted that many methods are implemented for calculating backpack capacity.

There is an existing standard for calculating backpack capacity documented at http://www.astm.org/Standards/F2153.htm however these standards are not enforced and this allows for a great variation between brands.

White Mountain Backpacks™, travel backpacks, hybrid backpacks, hike packs, daypacks, designers, wholesale direct, backpack fitting specialists, anatomically correct quality backpacks at the lowest prices. Backpack fitting experts specialising in FREE CUSTOM FITTING of internal frame travel packs, hike packs, and framed daypacks, including any brand purchased from other suppliers. To correctly customise and contour the Internal Staves of online orders, all we need is the correct Torso Length of your back. We offer premium quality, anatomically correct, high functioning backpacks at extraordinarily low prices when compared to any high quality competitor product, we guarantee exceptional performance, fit, comfort, and quality.