so it depends a little on what you want to store in your pantry, if it's only, like with nordlys, dry food and a few drinks then I agree with the dimensions. but as soon as a second fridge or freezer is to go in, the situation looks quite different, likewise if you want it to be so big that you can walk inside. if a device is to go inside and you want to walk in, then you have to choose the depth of the devices and a comfortable passage width as the width of the room, for most freestanding devices that means about 1.5m width (0.7 device + 0.8 passage, but everyone has to decide for themselves what is enough) the length then depends on the storage needs.
it's best if you write down each room you want to have separately, then think about what you want to put in there and how much space that takes up (sometimes the internet can help). in this way you can gradually find out what minimum size and/or what format the rooms should have. that’s how I proceeded. with the house it is quite okay to plan the walls around the furniture, with a rental apartment that’s not possible, there you mostly have to manage with what is already there. of course you should also plan so that a different furnishing is possible without having to change walls, but you get a feeling for which rooms need how much space for their function.