We are being asked what KVA we require for our new build. It is a 4 bed detached house? Any formula's tp work to per Sq mtr or similar?

You need to know how many electric showers, cookers, etc you have if heating is electric etc? Best way is to declare that all you need it a 100amp supply or work out KVa for a maximum 100amp supply. The cost of a new supply will dramaitaclly increase when you/if execed 100amps anyway. most domestic houses are 60 to 100amp max. As the other poster has said the formula is as follows; The total power S in kilovolt-amps is equal to current I in amps, times the voltage V in volts, divided by 1000: For most UK domestic propertives Maximum demand will be 100amps (I) and voltage will be 230 (V) S(kVA) = I(A) × V(V) / 1000 So kilovolt amps are equal to amps times volts divided by 1000. kilovolt-amps = amps × volts / 1000 So as a guide 100 x 230 = 23000/1000 = 23Kva Hope this helps

Most domestic installations have a 100amp main fuse provided by the electricity supplier. Therefore 100 amps x 230 volts = 23000 volt amps or 23kva.