Whether a Cable Is Big Enough, on Both Counts VOLTDROP
Four circuits bunched in a warm loft is not the worse of the two factors. It is both of them multiplied, and a cable at 94% of its rating should be at 75%.
The circuit
Three per cent for lighting and five for everything else is the ordinary pair, which on 230 V is 6.9 V and 11.5 V.
The cable, and what is done to it
The tabulated rating and the millivolts per amp per metre are yours, for your cable and your method of installation. They are not invented here: a capacity invented by a web page is a cable that overheats behind a wall.
Whether it passes
The working
Questions people ask about VOLTDROP