Here is an approximate guide as to how much space you will need. Remember, the more efficiently you utilise the space the less you will require (for example, storing cardboard boxes inside empty wardrobes).
House contents guide
1 Bedroom house = 50-60 sq ft
2 Bedroom house = 60-80 sq ft
3 Bedroom house = 80-150 sq ft
4 Bedroom house = 150-200 sq ft
Vehicle contents guide
Estate car = 16-30 sq ft
Transit van = 35-50 sq ft
Luton van = 60-80 sq ft
7.5 tonne lorry = 150-200 sq ft
Decorating? Room contents guide
Average Kitchen = 35-50 sq ft
Average Bedroom = 40-60 sq ft
Average Lounge = 50-60 sq ft
Lounge-Dining Room = 50-80 sq ft
Office, Archiving contents guide
30 Archive boxes = 16 sq ft
80 Archive boxes = 30 sq ft
100 Archive boxes = 50 sq ft
200 Archive boxes = 100 sq ft