Dining table in a small kitchen

So for me, that would not be fully developed yet. The guest room being larger than the kitchen for 4 people is simply not acceptable. My two children constantly want to help, and our 12m2 kitchen with a table and L-shaped kitchen is far too cramped. In the new house, the pure kitchen area will be 20 m2 and the guest room upstairs [im OG].

For me personally, it is difficult to estimate in advance what the required room size should be.

The fact remains anyway: the budget limits us, the plots here are already very expensive, and we simply cannot afford a 20 sqm kitchen and a 40 sqm living room... It's just not possible. On the one hand, I find it so intense that you invest half a million (including the plot) and then apparently only end up with a house with 20 compromises - that really depresses me. On the other hand, the lottery win has not happened yet, permanent rent over 1000 euros is not an option, and so we probably have to build according to what the budget allows... and that will not be a 20 sqm kitchen.

But I also don't think we necessarily need that. My parents and friends have 18 sqm. That seems very generous to me in both cases, furnished quite differently, with large tables inside; that much space is nice, but I wouldn’t need it.

With the 12 sqm, I see less the problem in the exact square meters and more in the room shape. It just needs to be wider.

The option of widening the house therefore seems sensible to us, but the annoying thing is that it's hard to widen just the ground floor - upstairs all rooms are sufficiently large for us and we would pay dearly for the additional space we gain there, which we wouldn't even need.

We will talk to the architects again about a bay window to make the living room a bit bigger if we widen the kitchen (guest) by 3 sqm at the expense of the living room. The children will probably play in the living room much longer, and especially there I don’t want to save too much space...

Another consideration; we could use the original kitchen space

A) as a guest room.
B) enlarge the living room by this area and then have a kind of play area for the little ones there.

Theoretically, we could also use my office as a guest room. We don’t have guests very often, and a sofa bed would probably fit in 11 sqm as well.

Or we reduce the almost 11 sqm kitchen to about 7-8 (that is enough for a cell with a sofa bed?), but can give these 3 sqm to the living room? Although that would affect load-bearing walls because of the shift...

But with the cost per sqm, everything inside me is now resisting creating an additional extra guest room. Overnight stays are simply too rare for that.

There is also the option of moving the staircase at the expense of the utility room and upstairs the bathroom. The bathroom can handle it, I find the utility room not particularly spacious for a house built without a basement.

Maybe a silly question, but have you ever taken graph paper, drawn the room, cut out the furniture, and just tried it out? Then you will quickly see whether what you want fits, or if in the end it’s just a room full of furniture, but nothing more.

Alternatively, there are plenty of free tools on the internet with which you can create that and even visualize it in 3D.

The question is not stupid at all no, I haven't yet. I haven't bought a kitchen or a bistro table, so at most I can calculate how big which piece of furniture could theoretically be. But I also don't know the sizes and swing areas of the doors. I think we will have to discuss that again with an architect.

But can you recommend a tool for that?

still no kitchen bought

But a kitchen always has the same depth, and if you roughly know how the kitchen should look, it's easy.

still no bistro table

I would go by what I want to have, not what is theoretically possible (topic compromises).

also don't know the sizes and swing areas of the doors

*ahem* well, standard doors always open the same way. For the kitchen it will be either 90 cm or 100 cm (clear width lintel/door width 86 or 96). So, no rocket science.

But can you recommend a tool for that?

I would really first recommend the manual method. With it you can also immediately sketch your plot, your house, your terrace, and position it on the plot.
The number of tools is large and also strongly depends on skills (examples: Home by me or SweetHome3D).

A few more words about other things I stumbled upon while reading:
Sliding door: this should then be an inside-running one (i.e. in the wall), which gets quite expensive if you want it to look nice.
Open kitchen: as already mentioned several times, as soon as there's at least one more guest, you sit in the living room anyway and then have to go around (I don't have the floor plan of your core house in mind). We currently have a completely open kitchen-living-dining area in our apartment. I wouldn't want to miss that. You can keep an eye on the child while cooking, be part of what's going on when guests are there. You don't always have to run somewhere for drinks. And beyond that, how small are the children? Do you want to carry the children's chairs around every time and possibly damage the walls?

Sorry, but when I read your post, I wonder what you have with all these m² specifications all the time. Of course, it is helpful as a guideline, but with you it slowly seems as if it absolutely has to be a certain "amount" of square meters to be enough.
m² are not everything; they only really come into their own if you can also furnish them properly.
I already experienced this myself in our planning that a children's room with 12m² was easier to furnish than one with the same layout but 15m². The only difference between the rooms was that in the smaller one there was space for a wardrobe behind the door, which was not possible in the larger room.
These are the things that matter in planning and not whether it’s 15, 18, or 20m². What use is a kitchen with 20m² of space if you walk yourself sore because the distances between the work steps are very large?

I therefore strongly recommend that you let go of the QM.

Approach it differently and try to develop a sense of space based on the furniture you need. A table 2x1m + 6 chairs (2 on the long sides and 1 on each end) alone would require 3.60x2.20.
If it’s only 5 chairs and you place the table with one short side against the wall, 2.80x2.20 is enough. The 2.20 is already dimensioned so that you can easily walk behind a chair if someone is sitting there. If there is a bench on one long side against the wall, it will be correspondingly less.
Just try googling "Tischfabrik Raumgröße Ratgeber." It helped me a lot.