The volume of travel bags

https://www.rei.com/product/794756/sea-to-summit-big-river-dry-bag-5-liters

Using this bag as an approximation it converts to about 300 cubic inches. So any combo of LxWxH that works to 300 will give you an idea of the size. For instance 6x5x10 inches. I would guess that’s about the size of a small packing cube.

5 liters if roughly 1.3 US gallons or 5.3 quarts

Picture how much space 1 gallon jug plus 1 quart more would take up in your suitcase.
Or picture how much you could fit into something a little bigger than a gallon jug.

As far as how they calculate the volume, I think I've read that there is an ASTM method for calculating the volume of luggage, but who knows if manufacturers really follow it.

With us, everyone travels with one 22 inch carry on bag with swivel wheels. And a small backpack or big purse. We try to stick to 22 lbs. maximum weight. With careful packing, we can travel indefinitely with that.

European rental cars are smaller and that's all their trunks will hold.

I remember all the husbands in the Venice airport one morning--hauling two 45 lb. big suitcases for their wives. I thought "you poor guys."

Everyone needs to be able to haul their own luggage on and off trains and public transit.

Thanks, everybody.

khansen, that sounds like a large amount of space. More than I had anticipated!

You need a bag, a garden hose and a 1L milk carton. ...

Why the garden hose?

Well, I probably should have mentioned the bags. Both are Briggs and Riley. One is the Rhapsody spinner underseat and the other is the Baseline spinner underseat. The measurements are almost the same but the capacity is different. How is that possible?

https://www.briggs-riley.com/products/cabin-spinner
https://www.briggs-riley.com/products/wheeled-cabin-bag

These the bags?

Someone cannot do basic math.

The interior measurements listed produce a result of 1670 cubic inches for the Baseline and 1695 cubic inches for the Rhapsody. A difference of 25 cubic inches ( 5 x5 x1 ; like an ipad mini folded in half)

Those are the ones, yes.
Thank you! An iPad mini folded in half is very easy to understand.
I'm terrible at math...

To figure volume, many manufacturers use the ASTM method.

They fill the bag with plastic pellets about the size of bb's. Once they have filled it full, they then put the bb's in a large tube with volume markings.

The reasons the measurements don't always "measure up," is because the material on soft sided bags gives a little. We've all seen that when we overpack.

1 liter= approx 61 cubic inches. 5 liter approx 305 c.u.in. 10x5x6.

https://www.briggs-riley.com/pages/store-locator

I would go look at them and see which one has the configuration that suits your needs

This is my under seat bag. As you can see we are worlds apart on the budget issue. :-)

https://www.eddiebauer.com/p/82300168/stowaway-packable-20l-backpack?sp=1&color=Tobacco&size=ONE%20SIZE&sizeType=

I wish I could go look at them but nobody around here carries them. I did see the
Baseline in a store at Heathrow last year but I don't recall seeing the Rhapsody.

Believe me I am combing the secondhand market like a true packing fanatic!

We just measured our new suitcase, calculated the volume and then compared it to the volume stated on the website.
We measure 72.3 L vs. the 97 L claimed on the website. That seems a lot greater difference than one would expect based on small pellets expanding the sides of a suitcase.

Michrad, that's a heck of a difference!

We just measured our new suitcase, calculated the volume and then compared it to the volume stated on the website.

What did you get? That is a stunning difference.

.Isn’t capacity (volume) the interior space not the exterior size. I have pondered how to calculate it without success. Anyone have a way to do so?

Joe32F SandraL

The capacities are published in the specs. The difference is about 1,472 - 1,121 = 351 cubic inches, not 25.

That would be the equivalent of 10" x 7" x5", about the size of a small toaster, not an iPad Mini.

Also note the weight of the empty bags. 6 to 7 lbs. would be pretty heavy for an underseat bag. If you intend to combine with a carry-on bag in the overhead compartment, you will probably exceed your weight limits.

A lot of weight and volume is wasted by all the hardware in most spinner luggage (wheels, handles, telescoping handle, padding, hard case, etc.

A backpack with more easily compressible shoulder and hip straps will minimize weight and maximize volume capacity.

Of course, you could go extreme and pack using a simple burlap sack.

I'm not a math person, so I don't even understand how
they determine the volume.

"Math person"? Yikes! His calculations are really simple geometry. For a rectangular solid V = L x H x W.

But that's kind of a theoretical starting point. It's the inside dimensions of an ideal sizing box. In actuality, you never get those ideal dimensions. An awful lot of bags are tapered from the bottom to the top, so you lose volume from the taper. Then there are the corners. Are they sharp, or rounded. You lose volume due to rounded corners and edges. And then there are pockets. People don't realize how much those handy outside pockets can cost them in total capacity.

And that would be for an ideal backpack. For a wheeled bag, add wheels and handles; they take volume. The tunnel inside a rolling bag for the handle to collapse into takes away volume. Spinners lose a lot of volume because the wheels extend an inch or more below the luggage and airlines count that towards the overall height, so the bag itself is shorter.

So, the theoretical maximum for a 22 x 14 x 9 inch bag is 2772 cu. in., but you lose hundreds of cu. in. of outside volume to those things I mentioned above.

And then there is the bag's fabric itself; it occupies volume. The six panels enclosing a 22 x 14 x 9 inch backpack are about 1300 sq. in. 500D Cordura is about .015 in thick (Amazon), so just the basic enclosure occupies about 20 cu in. Then there are inner walls, pocket walls, the strap pocket, etc. For a 3# backpack of 500D Cordura, the material occupies about 150 cu in.

And all these specification are generated, not by Engineering, but by Marketers, who probably have less math skill than SandraL.

The ASTM "capacity" is a perfect example. It allows the capacity (i.e., inside volume) to be greater than the specified outside volume, a physical impossibility.

everyone travels with one 22 inch carry on bag with swivel wheels. ...
With careful packing, we can travel indefinitely with that.

I think Rick once said something like he packs the same for a week as he does for an entire summer. I pack for about 3 days without washing clothes. With sink washing, I've gone three weeks. (One of the high points of my trips is the day I realize I have enough clean clothes to get me through the rest of the trip, and I can stop sink washing. Yay! But for me, the freedom of a really light bag is worth every minute of sink washing.)

funpig

The capacities are published in the specs. The difference is about 1,472 - 1,121 = 351 cubic inches, not 25.

When one does the math with the interior dimensions listed for each bag, the volumes do not match what they list as the volume for each bag. That is why I commented some one could not do the math.

Cabin Spinner:
INTERIOR DIMENSIONS
14.25 x 14 x 8.375 in /
CAPACITY
1472 cu in / 24 liters

Wheeled Cabin Bag:
INTERIOR DIMENSIONS
14.25 x 14 x 8.5 in /
CAPACITY
1121 cu in / 18 liters

If the dimensions are correct for each bag, then the capacity difference simply is a mathematical impossibility.

If the volumes are correct then the listed dimensions are incorrect.

The only other possibility is that the dividers in the one bag eat up more space than is evident from the photos, accounting for the wide variation of listed capacity, thus the suggestion to compare them in a store. ( OP reports there is no retailer close to her to do that)

Wow, this sure has turned into a lengthy thread!
Thank you all for your input.
If I buy one of these bags, it will be used as a carry-on. I will still check my TravelPro Maxlite 22" spinner.
I wish I were the sort of person who could use a backpack without back pain. Even just using a small one for a daypack bothers my back.

Get a backpack with a waist belt.

The eTech Weekender Jr., my bag of choice for the last ten years, came with a waist belt, which I never use because, at 12# (bag and contents, loaded), my backpack is really light, less than 50% heavier that a gallon of milk (do you really need a cart to take a gallon of milk to your car?).

Once, I affixed the waist belt to my bag which was loaded for three weeks in Europe, then loosened the shoulder straps until they were carrying no load, only keeping the bag from falling over on my back. All the load was supported on the waist belt and it worked!

Lee, I've tried backpacks with waist belts. Still doesn't help. I admit to having terrible posture, and being out of condition, which I am sure contributes to the problem.