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
How it works
VOLTDROP checks whether a cable is big enough on both counts: current-carrying capacity after correction factors, and voltage drop over the run. Correction factors for grouping and temperature multiply, so a few circuits bunched in a warm loft can overload a cable that looks fine. It compares the cable with the protective device and gives the longest run allowed. The figures stay in this tab.
Doing this often? Foundry, the Engineering Suite's drawing half draws the cable runs to scale, with dimensions, and prints a PDF to scale or saves DXF. On its own, US$4 a month; with everything else, US$9 a month or US$79 a year. 7 days free.