IF I want to be strict about 40x30x15 cm backpack rule

I have this one.

https://www.amazon.com/Rangeland-Business-Backpack-Approved-Daypack/dp/B07B7G22FF/

Pros: Cheap. Opens like a suitcase so easy to pack and holds alot. Has a good external pocket for either laptop or Ipad.
Cons: Straps aren’t my favorite and it doesn’t have a side pocket for a water bottle.

I have 2 of what Laura describes. The oldest is 12 years old. One or the other used every trip. No defects at all. 1" too big for some fights, 1" too small for others. All about how you pack it.

The Patagonia terravia tote pack is very close and will work.
With bag dimensions like these, about 23 - 24 liters, a tote pack may be a good choice. Stay with a large main compartment and only a couple of external pockets. Use packing cubes. Avoid multiple compartments and pockets.

I have an Osprey daylite 26 that is a tiny bit bigger than your desired dimensions (17 x 13 x 6 inches) when not expanded.
Are those dimensions from Air France? I must say, it is hard to find a bag that small.
I did fly on Air France twice within the last year and did not have any problem with my backpack. But I understand you are looking for something even smaller, and probably cheaper.

I'm actually interested in responses here since I need to purchase a new personal item backpack for my teen, and the Osprey is a bit big for her size.

I also have the Osprey Daylite 26; I didn’t suggest it because it is bigger than 16 x 12 x 6.

Pros: Opens like a suitcase so easy to pack. Expandable. Has a water bottle pocket.

Cons: Too big to be used as a personal item on many European airlines. The laptop compartment is within the main compartment (although accessed via a separate zipper) and I find it difficult to get my Ipad in and out of that pocket when the suitcase is fully packed. I find the straps a bit stiff.

If you go to Amazon, and put 'backpack 40 x 30 x 15 cm" in the search bar, a few different ones will appear. You don't need to use the quotation marks.

These bags are commonly found in Europe but not popular in the US due to their smaller size. You have to search in centimeters rather than inches.

Someone else on the Forum recommended the Columbia Convey 24L, which is on clearance at Sierra.com. It's a little too tall, but if it's not full, it should squish down enough.
https://www.sierra.com/columbia-sportswear-convey-24-l-backpack-metal~p~1uvmc/?filterString=daypacks~d~9670%2F
I've also seen the Sherpani bags mentioned a lot. Here is the Sedona, which is only 16L but fits well within the dimensions given:
https://www.sierra.com/sherpani-sedona-backpack-raven~p~5wpad/?filterString=daypacks~d~9670%2F
It also comes in a sort of grey-and-tan color way.
That 6in/15cm dimension is difficult to find, in seems.

I have researched and have a few options, but would like to know what you have found.

OP - it would be great to see which ones you have found during your research.

I reached out to a friend who travels a lot on European budget airlines. Her personal item backpack is this one.

I reached out to a friend who travels a lot on European budget
airlines. Her personal item backpack is this one.

Which is too large for Wizz and Ryan who make up most of the European budget flights. Always check the airlines you are flying and consider their rules.

In my own research, I came across the Patagonia Atom 20L Tote Pack which fits your desired dimensions. But the cheapest I saw was $95 for solid black or $70 for a colorful one. I'm more interested in the new Atom 24L (non-tote) but it is a tiny bit bigger but I think can be easily squished to fit your dimensions.

If you haven't purchased a bag, I just bought a packable backpack that measures 41 x 28 x 20 cm. (It's packable so it scrunches down.) I'm impressed by the quality. The only two things I wished it had were a water bottle pocket and a luggage pass thru.

I got it onsale in Germany for just over 18 Euros ($21.) It's a little more in the US. Mine is black.

Go Travel Lightweight Foldaway Backpack

Hey Frank II,
There’s a similar bag on Amazon. I think a basic roll-top could suffice, as well. Just be careful of filling up the top area too much. Any squishy, packable pack under 25 liters would probably work.

Fitkicks Hideaway pack and Brand Coscooa on Amazon. There’s a few others, not many, on Amazon.

General update:

There are a few options on Amazon with these specific measurements. I might order one or two to see how they look.
I already own these options now which could work if I don't adhere to the strict dimensions and/or don't overpack.
Duer Backpack: 18 x 11 x 7 (46 x 28 x 18cm)
Foldie Tote: 17.8 x 10 x 8 (40x32x16) not expanded

Options meeting strict Air France standards:  
Patagonia Atom 20L 16x12x5 (Day pack 24L = 16x12x7)  
Fjallraven Kanken 16L 36x28x12

Close options:
Patagonia terravia tote pack 24L 16x10x8 (over in width and length)
Fjallraven High Coast Crossbody 23L 40x31x14 (very close) 15.7x12.2x5.5
Osprey Daylight 26 17x13x6 unexpanded (over by an inch in height and width)

MT - Helpful to see this detailed list. Thanks for returning to share.

I'm surprised no one, including me, has mentioned the Rick Steves Oslo Backpack. It's pretty much 40 x 30 x 15 cm.

https://store.ricksteves.com/products/oslo-backpack?variant=46199742333084

If you are in no rush, these usually go on sale a few times a year.

The Oslo pack at 17 liters would make a great day pack. If OP is going to pack clothing and needs every liter of space possible, then the Patagonia terravia at 23 liters would be better. I do like the design of the Oslo.

I think a tall man might find the bag rather short and not laying in the lumbar area of back. For women under 5’6”, the torso length is good. The civita works well, because it is a “saggy” bag. That is, the straps can be adjusted until the bag lays low on the back.

I just found LLBean stowaway tote pack in blue and black. Dimensions are good. About 23 liters. Minimalist attitude.

I've been traveling for years with a Sherpani Soleil:
newer black/gray version

For me, I like that it is a tote, backpack or crossbody, because it provides me with quick and easy options while getting off/onto transportation. Mine also has a trolley strap on the back and the tote handles work great when I use it on a two wheeler in the 'add a bag' position. It is BA compliant, which is important to me, but I use it as my personal item for most trips. Mine still looks like new. I wish mine had the light interior that this one does.

I'm surprised no one, including me, has mentioned the Rick Steves Oslo Backpack.

It is a little above the desired dimensions, like a few other contenders. I'm still searching, as well, for one for my teen. She currently uses a school backpack when traveling and enjoys the easy access pockets at the front. But finding one that is personal item compliant, light, with trolley sleeve and without breaking bank is harder than I thought.

If you have this back you listed, "Duer Backpack: 18 x 11 x 7 inches", just use it and don't buy another backpack if you don't have to.

If you have to buy another backpack, among the brands you listed, one of the Fjallraven models is what I would pick.

I would pick a backpack with two backpack straps, not a crossbody bag with just one strap, and not the tote bag style that looks like a fancy reusable grocery bag or a purse.

In my experience, the daypacks that are really thin that can fold into taking up about 5 x 5 x 5 inches or a bit more or less, are crap and a waste of money. They can't handle the weight of ten euros of coins and an approximately 50 ounce full bottle of water.

I took multiple plane trips using a Jansport school backpack as my carry-on luggage. In August 2024 on a trip to Germany I took through security a 19-inch duffle bag with a single strap, a Jansport backpack, and a reusable grocery bag with some food I didn't want to get crushed. At the last minute before getting on the plane, a staff member said I had to combine my stuff into just two bags if I didn't want to check something in. I stuffed the contents of my reusable grocery bag into my Jansport backpack and forced the zipper closed. When the plane arrived, I discovered an approximately 1-1/2 inch tear along a seam of the backpack. I wouldn't buy any backpack that seems less heavy-duty than a Jansport. Jansports are probably medium duty. Any backpack could break if you stuff too much volume in and force the zipper closed and/or if you put in too much weight. A small Jansport backpack would work good as a day backpack. I bought a Queckua backpack at an outdoor and camping store in Germany. The padding on the back is quite nice. But it is meant for hiking, not planes. It fits fine in the overhead bin but it does not fit under the seat. I do not use the Quechua as a day backpack.

You don't have to look for excuses to buy another piece of luggage. Inspect what you have. If it is intact and can do the job, just use it and don't stuff it too full.

@Joy,
Not breaking the bank, I hear you. Inflation has pounded everyone the last few years. Set a budget and try to find a sale price for item you desire. Look at various sites. Be willing to purchase an ugly color.
There are some decent bags out there. But, the time has come to stick with basics.

Thanks everyone. I’m still in the process of figuring it out. We are a family of 4 so trying to use what we have and maybe buy 1-2 budget options for the personal bag requirement, but it’s true…you get what you pay for.

Be willing to purchase an ugly color.

Well, that won’t sell with my kid. She likes basic like black and nothing too bright. I found a backpack today at Marshalls that will work for my kid. And only $40. I know a bit taller but can easily be squished down.
I found at the store but saw online: https://m.marshalls.com/us/m/jump/product/Bianca-Xl-Backpack-With-Insulated-Pockets/4000415462?colorId=NS11987316&pos=1:1&Ntt=Backpack

@OP,
“You get what you pay for.” True. But, the good news is cheap bags can and do suffice much of the time.

Sun-Baked in Florida, if my $40 bag died tomorrow that would be 45 trips over 15 years. So the $160 bag would have to last 180 trips over 60 years. That makes me about 130 years old when the zipper breaks. Google, "law of diminishing returns". Now, if i just love it, well, that's priceless. Nothing else matters.

I purchased an EcoHub underseat travel backpack from Amazon. The trolley sleeve kind of sucks, but there’s a water bottle holder, opens like a suitcase, and tons of pockets for organization. Up to 30L and weighs 1.6 lbs. $35-40, but often on sale for $30.

The eco hub one is technically just off of the measurements (it's 17x10x9 and I'm looking at 16x12x6).

I'm probably going to use a bag that is slightly bigger because I don't plan on stuffing it.

I ordered 3 to check out and compare (from Amazon).

https://www.amazon.com/dp/B0FJDSH8Z1?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1 (coscooa brand)
https://www.amazon.com/dp/B07B7G22FF?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1 (Rangeland brand)
https://www.amazon.com/dp/B0FS1KSGXH?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1 (Nixjoro)

Mr. E,
The ever evolving luggage allowances by airlines and increasing travel experience have led me to the “less can be more” way of thinking. I’m not a total minimalist. I have learned that simplicity and the concept of good enough can often get the job done. It is fun to splurge and have nice things. However, sometimes a simple cinch or roll top type bag with some back padding and straps will do just fine.

I stress understanding your own travel needs, your comfort budget, and creating your own specific criteria for purchasing a bag. Too many lists for business men; And, I do mean men hauling computers and other electronics, etc.. I have sympathy for new travelers trying to figure out which way to go. For me, figuring out bag liters and what that meant for packing was a challenge. Now, many bags later and I understand.

Sun-Baked in Florida, I live a typical Eastern European life, which means compact and spartin. Most Americans have no idea ... I am blessed and can do it by choice.

My personal item bag was about $20 when I bought it but now Amazon sells it for $35. Outrageous. Perfect size and shape for the intended task. No flaps or stitched on pockets, just a cube and a couple of straps. My newest addition is my WizzAir compliant four wheeler. That was almost $35 at an Asian import no-name junk shop. So far 4 flights, so far no issues. Perfect legal size. Both unique colors for quick identification at Canadian airports.

Now, I do have an expensive as heck small crossbody bag for passport, phone and pocket junk at airport security. Its the exception. I like it so I dont care that ounce for ounce it cost 10x what everything else cost. And I get the designer bag folks. I love to fly fish. Fly fishing is about technique and skill first and second, then third its about the equipment. I am not so good that I will fish any better with a $1000 rod than I will with a $400 rod. Of course, its my love so I have the $1000 rod.

I do have quite a few failed attempts. I give them away to friends traveling when ever possible. One is leaving in a couple of days, I hope to never return.

Right now, I’m set with a plethora of bags. If I traveled to a rainy climate (worse than Florida), I would consider getting the cheapo Marchway dry bag backpack on Amazon.
Years ago, I bought a cheap 2 wheel suitcase on clearance at Sears. (I’m really dating myself like carbon dating.). $20. Not a brand name, not even Sears. I cannot kill the bag. I have abused the bag.

With today’s inflation, getting a less expensive option seems the way to go. These bags will work!

Adidas Alliance sackpack. About USD$15. Lightweight, sturdy, holds up to 12 L. Athletic style, lots of young people carry them in Europe. 2 outer mesh pocket. One zippered pocket. Easily stuffs into carryon luggage. Lots of colour choices.

https://www.amazon.com/adidas-Alliance-Sackpack-Black-White/dp/B00GV47ZGQ

I was looking at backpacks on Amazon and saw this:

https://a.co/d/01BfNagD

It's the exact measurements you want. (Ignore the "inches" and stick with the cm's as they usually round up with inches rather than exact. It's also on sale if you have Prime.

Frank II, its a lovely bag, but everyone of those people in their photos has overpacked the bag to the point that it will not fit the bag sizer.

This is all about style as anything else. I just packed my $30 Rangeland bag for my trip to Montenegro tomorrow (you know the one) and while it isnt stylish it is almost a perfect cuboid meaning it has the maximum amount of interior space given the greatest dimension in each direction. Having no sense or style or aesthetic taste I went for efficiency.