So I've packed my teeny tiny cabin bag

[GreyBlossom]

For Wizzair. 20x30x40 cm.

I was quite pleased with myself because everything fitted with room to spare.

However, whilst the fixed edges of the soft rucksac may well meet the dimensions, clearly once packed it doesn't. It's 2-3 cm over in all directions.

How much will matter?

Anyone?

You say it still has room in it, will it wiggle about to fit the correct dimensions?

Oh & to answer your question. It'll depend who you get!!

Depends on whether they make you put it in one of those cage things to check at the airport. Will it squeeze down?

I had similar a while ago, no one checked and I just walked through with rucksack on my back. It fitted easily under the seats front.
if you are worried can you wear a couple of extra layers for boarding so the bag squashes down a bit? Or put stuff in pockets?

It very much depends on what happens at the airport on the day. You are probably better off to reduce it slightly. If it can squish down to the correct size you are OK, otherwise you venture into the unknown. Do you really need those extra awkward bits?

Which airline are you flying with? If it’s a soft bag then you’ll be fine as you’ll be able to squash it into the measuring cage - that being said I’ve never had to have my bag size checked in all these years although I do realize this is down to luck.