External dimensions lie: how we measure real bag capacity (25×17×14 ≠ 5.95L usable)

Short answer: a 25 × 17 × 14 cm bag measures about 5.95 L by its outer dimensions but packs to roughly 4.8 L of usable volume — about 19% less, because wall thickness, seams and curvature all eat into the space. Discount any external figure by 15–25% for a structured bag, and about 10% for a soft one.

The number on the box is not the number you pack

A bag listed as 25 × 17 × 14 cm has an external volume of about 5.95 litres. But you cannot fill a bag to its outer walls. Real usable volume is smaller, and the gap between "external" and "usable" is exactly where most buying mistakes happen. Here is how we actually measure it.

Step 1 — measure external, honestly

Close the bag, let it sit naturally, and measure the three outer extremes: longest point × widest point × deepest point. For the Jelkin 25 Cloud that is 25 × 17 × 14 cm. Multiply: 25 × 17 × 14 = 5,950 cm³ ≈ 5.95 L external. This is the ceiling, not what you get.

Step 2 — subtract what you cannot use

Three things eat into external volume:

• Wall and structure. A structured (sellier) bag has a built frame. On a 14 cm depth, the rigid base and turned edges can cost 1–2 cm of usable depth.
• Curved sides. A rounded bag looks bigger outside than its flat packing area inside.
• Dividers and pockets. Internal zipped pockets are volume you cannot merge with the main compartment.

Net effect: usable volume is typically 15–25% below the external figure for structured bags. A 5.95 L external bag often packs like a 4.5–5 L one.

Step 3 — the rice/bean test (the only honest method)

Forget the maths. Fill the bag with dry rice or beans using a measuring jug, pour it out, and read the litres. That number is your real capacity. We did this with the Jelkin 25 Cloud and it packed to roughly 4.8 L of loose fill — about 19% under the external 5.95 L, exactly in the expected band for a structured bag.

Why this matters for "will it fit my stuff"

Two bags with identical external dimensions can have very different usable space. A soft, flat-walled tote keeps more of its external volume; a structured bag with thick edges keeps less. When a listing only shows external size, you are comparing ceilings, not reality.

The sizer trap

Airline sizers measure external size including handles and wheels. A wheeled bag at "25 × 17 × 14" externally may actually be 27 cm once you add the trolley handle housing — and fail. A soft structured bag like ours keeps its external number honest because there is nothing to add.

Our rule of thumb

When you read "fits under the seat", check the usable number, not the external one. If a site only gives external dimensions, discount it by ~20% for a structured bag and ~10% for a soft one. And if you want certainty, do the rice test yourself — it takes five minutes and ends the guessing.

Method note

External dimensions from product specification. Usable volume by fill test with dry rice and a 1 L jug. Airline sizer rules from official baggage pages (October 2026).

Questions people ask

How many litres does a 25 × 17 × 14 cm bag really hold?

About 4.8 L of loose fill. The external maths gives 5.95 L, but a rice-and-bean fill test on the Jelkin 25 Cloud came out roughly 19% lower — inside the 15–25% band we expect for a structured bag.

Why is usable volume lower than external volume?

Three reasons: the fabric and lining have thickness, the seams and base panel take up space, and a filled soft bag curves, so the corners never pack. A structured bag loses more than a soft one.

How do I measure usable volume at home?

Use dry rice or beans and a 1 litre jug. Fill the bag the way you would normally pack it, pour the fill out into the jug, and read the total. It takes about five minutes and ends the guessing.

Should I trust the litre figure on a product page?

Only if the brand says how it was measured. Most quote the three external dimensions multiplied together, which is the ceiling rather than the usable figure.

Go deeper: see the 25 cm bag that fits every airline sizer for the external-dimension side of the same argument, check any allowance in the airline personal item size checker, or read what actually fits in a 25 cm bag. The bag measured here is the Jelkin 25.