Cable Calc UK is a must have for all electricians.
This tool asks you the key information about the circuit, it will then do all the calculations based on BS7671 for you and return the correct size cable.
It will also check the cable for load and volt drop the tell you the correct MCB size.
While we believe this to be an accurate tool, you should always double check the results yourself with BS7671.
Some bug fixes
Up to six family members will be able to use this app with Family Sharing enabled.