Flying and suitcase weight

Travel light number is my advice. 20kg is a lot to lug and you won't use it all when you get there.
The strictest big airline I came across was Virgin Heathrow that had a limit of something like 6kg for carry on. "Go away and come back with a lighter bag"
Blooming bag weighed about 5kg.
Cue me stuffing books in my waistband, phone chargers in my pockets etc before returning with virtuous smile on face.

I was just going to say that - check the measurements as well as the weight! Every airline has different requirements. And yes, two cases.

It is also interesting what passes as hand luggage, and what some people manage to take on board. (Not with Easyjet and co, though.) My smallish wheelie bag holds a lot, and is classified as hand luggage. BUT measure and weigh it!

Number. As others have said, baggage allowance differs with each airline, but it's mostly 40kg per person for long haul, and 20/22kg. for short-haul. Carry on cases/bags are almost all limited to the same size - 114 linear cms. There are also a lot of restrictions with what you can pack in carry on.
If I were in your position, I'd divide what you need to take between the two cases. Much easier to manage.

The last couple of years OH and I have travelled to Europe with both EasyJet and Jet2 (Jet2 have 2kg more baggage allowance - 22kg) and we have no problem with one suitcase, usually weighing in at around 18kg or so. We were away for 2 weeks in June and found we had plenty of clothes, shoes etc for us both in one case.

We put books, Kindles, etc in our hand luggage.

So far, thankfully, our case has not been lost in transit!

If you are going with a budget airline - Ryanair, Easyjet. Jet2 etc they are becoming increasingly mean regarding luggage. I made a "Sod off Ryanair" jacket last year as so far they do not weigh what you are wearing. I bought a sleeveless mans zip up jacket with lots of pockets on the outside for 4 pounds from a jumble sale. Needs to be sleeveless with deep-ish armholes so it can be carried on one shoulder if need be. On the inside I added some deep pockets zipped along the top - the back one divided down the middle. I managed, by squashing all my clothes into zip lock bags (I do travel light ) to get almost all my clothes into the jacket (I think it weighed about 5kg)leaving room in the carry on case for such things as a fabric screen castle for the boys bunk-beds,English story books etc etc. I have 3 DGS in Spain as well as the 2 here in Beijing ! A bit of a multinational family !

Another Ryanair TIP !!
Never pay for priority boarding etc unless you really want to sit with family etc, especially if you like me mostly travel alone. Never join the queue which seems to start before the plane is on the tarmac. Sit back and wait and try and get on last. I have had back row seats (so first off the plane and through customs - 5 mins to the arrivals lounge is my record), Front row seats (ditto off first but also lots of leg room) and exit aisle seats (more leg room)
Just remember that if you are on the same flight as me then I get on last !!

Even if you're allowance is 40 kg or more, most airlines are pretty unenthusiastic about one bag of that weight and prefer it to be split between two. (It's impossible to lift and a real pain in the shoulders to wheel along anyway.) You can usually find out about the baggage allowance on the airline website before booking – different airlines and even different routes vary. These days the airlines tend to be very strict about the maximum weight allowed, even for short haul fllights.

Sorry Number but one case is classed as belonging to one person so if your hold allowance is the usual 23kg you cannot put more than that and say it is for 2 people. All airlines have different rules regarding luggage allowances and sizes of cases therefore please check carefully when you book your ticket.
I totally agree with Tegan about taking 2 cases and putting a mix of clothing from both passengers in each then at least if one does go missing you have a fighting chance of having something else to wear ! And ALWAYS carry spare knickers in your hand luggage. I speak from experience and know that my friend is much smaller than me in the knicker dept ! Another very useful tip is to take some photos of your cases before you set off so that if you ever have to fill in a missing luggage form you can at least remember what they look like !
Have a very good holiday !

Tegan, we haven`t decided on anywhere yet, but as we`re selling the caravan, and downsizing the car (due to advancing age and decreasing fitness!) we thought we`d have, next year, what will probably have to be our last good holiday. We`re considering a cruise, albeit one of the less expensive ones, but are also looking at Cruise and Stay holidays as well, which is where the flying question comes from. The reason I asked was that we don`t really want to buy new cases now, but all we have are 2 large ones, and were hoping to fit everything in one.

number; I don't even know what you can take in your hand luggage these days. I do reckon, though, that it's better to have two smaller suitcases and split everything between the two in case one goes missing [although, I suppose that increases the risk of one going missing by somethingorother % [maths not my strong point]]....where are you planning to go to? We're thinking of flying somewhere next year as well, not having flown anywhere for years.