Bag Calculator: Volume, Fabric & Carry-On Check
Enter your bag dimensions to get the total volume, practical usable capacity (accounting for packing inefficiency), the fabric surface area you need to cut, and a carry-on compliance check against the most common airline limits. Switch between inches and centimetres, adjust seam allowance, add a gusset, and choose your bag type. Results update instantly as you type.
Formula
Worked example
A tote bag measuring 14 in × 5 in × 13 in: Volume = 14 × 5 × 13 = 910 in³ = 14.9 L. Usable capacity = 14.9 × 0.82 = 12.2 L. With 0.5 in seam allowance and 15% waste on a 44 in bolt, fabric needed is about 0.95 yd.
What the bag calculator computes
This tool calculates four things from your bag dimensions: total interior volume in litres and cubic inches, practical usable capacity after subtracting structural dead space, the fabric surface area you need to cut (with your chosen seam allowance), and estimated yardage from a standard bolt. If you enable the carry-on check, it also compares your dimensions against popular airline limits. All results update as you type, so you can quickly try different sizes.
How bag volume is calculated
Interior volume is simply length multiplied by width multiplied by height. Because bag interior dimensions are usually measured in inches, the result is in cubic inches first, then divided by 61.024 to convert to litres (the unit most travellers and manufacturers use). Usable capacity is lower than total volume: rigid walls, zips, frame boards, padded panels, and inefficient packing geometry mean you can never fill 100% of the geometric space. The calculator applies bag-type factors: 75% for suitcases (lots of frame and padding), 78% for backpacks (frame sheets, hip-belt pockets), 82% for totes, 85% for duffels, and 90% for unstructured storage bags.
Calculating fabric yardage for a bag
To estimate how much fabric to buy, the calculator treats the bag as a rectangular box and computes the total surface area of all six faces, adding your seam allowance to each dimension first. It then scales up by your chosen cutting-waste percentage (10-20% is typical for bags, where you might cut handles, pockets and lining from the same piece), divides by the bolt width to get a linear length, and converts to yards. This is a conservative estimate - complex bag designs with darts, pockets or shaped panels will need more.
Airline carry-on limits explained
Most airlines measure carry-on bags as the total of length plus width plus height, or they state a maximum for each individual dimension. The calculator checks each dimension independently (sorted largest to smallest) against the airline limit. IATA recommends 21.5 x 13.5 x 7.5 inches (55 x 35 x 20 cm) for small overhead bags, while US carriers like Delta and American allow a slightly larger 22 x 14 x 9 inches. Budget European airlines such as Ryanair and easyJet have stricter limits. Always verify with the airline before you fly, since limits can vary by route, fare class and whether the bag goes under the seat or in the overhead bin.
Common bag sizes and volumes
| Bag type | Typical dimensions (in) | Approx. volume | Use case |
|---|---|---|---|
| Mini bag / clutch | 8 x 2 x 5 | 1-3 L | Evening wear, essentials |
| Tote bag (small) | 13 x 4 x 12 | 5-10 L | Daily shopping, gym |
| Tote bag (large) | 18 x 6 x 15 | 15-22 L | Work, beach, groceries |
| Backpack (day) | 12 x 6 x 18 | 18-25 L | School, hiking day trips |
| Backpack (travel) | 14 x 9 x 22 | 30-40 L | Cabin luggage, weekend |
| Duffel (small) | 20 x 10 x 10 | 25-35 L | Gym, sport |
| Duffel (large) | 24 x 12 x 14 | 50-70 L | Travel, moving |
| Cabin suitcase | 22 x 14 x 9 | 35-45 L | Short-haul flights |
| Checked suitcase (medium) | 26 x 18 x 11 | 65-80 L | International travel |
| Checked suitcase (large) | 30 x 20 x 12 | 90-120 L | Long-haul, family trips |
Typical interior dimensions and approximate volumes for standard bag categories.
Frequently asked questions
How do I measure a bag for volume?
Measure the interior - not the exterior - of the empty bag using a ruler or soft tape measure. Lay a rigid ruler inside and read the longest horizontal dimension (length), the shortest horizontal dimension (width or depth), and the vertical dimension (height). Measure at the widest points inside, ignoring seams. For soft bags, gently push the sides out to a natural shape.
What is usable capacity and why is it less than total volume?
Total volume is the pure geometric space (L x W x H). Usable capacity is the practical packing space after accounting for the bag structure: frame boards, padding, zips, internal pockets, lining, and the dead corners that are hard to fill efficiently. A rigid suitcase typically loses 25% of its geometric volume to structure and inefficiency, while a duffel bag loses only about 15%.
How much seam allowance should I use for a bag?
The most common seam allowance for bags and accessories is 0.5 inches (1.2 cm). Heavier fabrics such as canvas or denim sometimes use 0.75 in (2 cm) so there is more material to hold the seam firmly. If you are following a pattern, use the seam allowance stated in the pattern instructions rather than this calculator default.
How many yards of fabric do I need for a tote bag?
A typical medium tote (14 x 5 x 13 inches) requires about 0.8-1.2 yards of fabric on a 44-inch bolt, including seam allowance and a 15% cutting waste allowance. Larger totes or those with pockets and lining will need more. Use this calculator with your exact measurements for a personalised estimate.
Do airlines measure bags in litres or in dimensions?
Airlines always measure carry-on bags by their physical dimensions in inches or centimetres, not by volume in litres. The litre figure is a convenience metric for comparing bags, but at the airport the check is always a dimension gauge or a manual ruler measurement. The carry-on compliance feature in this calculator uses dimensional limits.
Why do different bag types have different usable-capacity factors?
Structured bags lose more space to their own components. A hard-shell suitcase has a solid frame, a lid that does not compress, and thick padding on all sides, so typically only 75% of its geometric volume is usable. A soft duffel has no frame, thin walls, and flexible ends, so about 85% is accessible. Backpacks sit in between because of their frame sheets and moulded back panels.