How do you work out Size of a house from room dimensions?

Hi
Looking at a house and have each room dimension in inches and feet. To work our overall size is it a matter of multipling each room dimension ie berdroom 1 10 x 15 = 150 and adding all rooms together?

There is no standard for this. EAs do whatever suits them. I lived on a road of identical houses adn they all had a different area, when they came up for sale.

You can add all the rooms together, including the hall and landing if you want more accuracy.
you could also measure the outside wall and do an overall area calculation.

EA's I think take full external measurements to maximize the sq footage, so the total of internal rooms, excluding alcoves and corridors with be much less.

Its normal practice to take the size of a house as everything inside the external walls. This will include the internal walls, alcoves etc. So just taking the room dimensions will give you a smaller answer

Wildhoney: thats exactly how you do it, its floor area of a house you want, walls don't count

2 schools of thought on external wall though. Which is correct - incllude or exclude ?

Its habitable living space. Therfore no walls or corridors. Multply width by bredth and add them up of the rooms this is the correct figure.
However since the EA have a habit of employing people with no relevent qualifications to do residential stuff you get wild calculations. I have come accross houses that have unconverted garages included in floor area. But the best one was I was looking at a house for a friend it was a villa style property it was slightly different in that it was buit on a hill so had two storys at the back but only one at the front of the house. The E/A had measured the square footage of the top floor of the house and multplyed it by 2 thereby increasing the square footage by 25%.

Be aware that most E/A's you meet no nothing about property and alot about marketing generally you are wasting your time asking them anything about the property. Take your own measurements and your own compass.

take external measurements in width & depth and subtract 2feet from both measurements and multipy to get internal area. This will give you a very good rough idea of internal habital space. Alternativley you could just use the external measurements

The "standard" measurement - if there is such a thing - may be to some extent influenced by the standard used down the years by the Department of Environment.

In deciding if a house is under or over 'grant size' (though the grant no longer exists) they measure the gross internal floor area. If you search their website, you will probably find a detailed set of rules for this.