Suitcase size calculator: capacity for your trip length

How to work out what size suitcase you need

The capacity you need is a fixed allowance for toiletries and shoes plus the clothes for each night, times the people sharing the suitcase. The calculator starts from 10 L for toiletries and shoes plus 7 L a night in summer, 9 L in spring or fall and 12 L in winter.

The starting point is the rule of thumb from moln, a Japanese luggage brand: about 10 liters per night, with a chart that runs from 30 L or less for 1-2 nights to 61-80 L for a week and 81 L or more from 10 nights. A 10 L allowance plus 9 L a night lands every trip length inside its band. The summer and winter figures are our own assumption, for light clothes or for sweaters and coats; moln itself advises a slightly larger suitcase in winter, and Samsonite's size guide says cold-weather travel needs more volume. You can change all of them in the advanced options.

If you do laundry on the trip, clothes are counted for 7 nights at most (also in the advanced options): after the wash you pack the same clothes again.

The calculator then picks the smallest size that holds that capacity. Above 120 L, the top of a large suitcase, it splits the volume into several suitcases of the same size.

Capacity is shown in liters in the US too, because that is how spec sheets list it: Samsonite's guide says capacity is usually measured in liters, Travelpro lists 46 liters for its 21" carry-on and Delsey 76 L for its 27" medium.

A worked example

In the US. The calculator opens with 7 nights, one person, summer and no laundry:

• Clothes: 7 nights × 7 L = 49 L
• Toiletries and shoes: 10 L
• Total: 59 L

That is more than the 45 L of a carry-on and less than the 80 L of a medium suitcase: you need a medium suitcase of 24-26" with at least 60 L. Two people in winter for 7 nights need (10 + 12 × 7) × 2 = 188 L, more than the 120 L of a large suitcase: 2 large suitcases of 28-30" with at least 94 L each.

In the UK and elsewhere. The same week is the same 59 L: a medium suitcase of 65-70 cm, at least 60 L. Fourteen nights in spring or autumn take 136 L, so 2 medium suitcases of 68 L; with laundry halfway through 73 L is enough, one medium.

Suitcase size chart by nights and season

One person, no laundry, with the starting values:

Nights	Summer	Spring or fall	Winter
2	24 L, carry-on	28 L, carry-on	34 L, carry-on
3	31 L, carry-on	37 L, carry-on	46 L, medium
5	45 L, carry-on	55 L, medium	70 L, medium
7	59 L, medium	73 L, medium	94 L, large
10	80 L, medium	100 L, large	130 L, 2 medium
14	108 L, large	136 L, 2 medium	178 L, 2 large

A weekend always fits in a carry-on. A week takes a medium suitcase in summer and a large one in winter.

Suitcase sizes on sale: inches, centimeters and liters

Suitcases are sold by height, measured with the wheels and handles, and the spec sheet gives the capacity. In the US Samsonite's guide puts carry-ons at 18 to 22 inches, medium suitcases at 23 to 26 and large ones at 27 to 30. The calculator uses 21-22", 24-26" and 28-30", with 35-45 L, 60-80 L and 90-120 L. A 27" case sits between medium and large: Delsey's 27" Helium Aero is 76 L inside, a medium by capacity.

In the UK and Europe the same sizes are 55 cm, 65-70 cm and 75-80 cm. Some spec sheets: Samsonite C-Lite 55 cm 36 L, 69 cm 68 L and 75 cm 94 L; American Tourister Flytwist 78 cm 101 L, 117 L expanded.

Carry-on size limits and checked bag weight are set by each airline and change over time: check your airline's current rules before you buy.

Common mistakes

• Choosing by height alone. Two cases of the same height can hold different volumes because width and depth change, as Samsonite's guide points out: check the capacity on the spec sheet.
• Counting the expansion zipper as space you always have. Expanded, a carry-on can go over the size your airline allows in the cabin.
• Packing clothes for every night of a long trip. With laundry halfway, 14 nights in spring or fall drop from 136 L to 73 L.
• Forgetting the trip home. Gifts and shopping take space: leave some room or raise the liters per night in the advanced options.
• One huge suitcase for two. Fully packed, a very large case easily goes over the checked bag weight limit, as Samsonite's guide also notes: two smaller suitcases are easier to handle.