How many & what size velux roof windows for room in loft?

wookie6

Hi,

I have tried using the Daylight Calculator on the Velux website (https://www.velux.co.uk/projects/daylightcalculator) to see how many & what size velux roof windows would be needed for a loft room. The recommendations seem massively over the top based on the 20% daylight figure they use, and another room in the house that already has a roof window much smaller than those recommended that is more than adequate.

From personal experience, can anyone recommend how many & what size velux roof windows would be suitable for a room in loft which has a floor area of 13sqm (only counting area of the floor where the ceiling height is more than 1.5m), where the roof windows will only be on one side of a 4m wide room where the ceiling slopes down.

Thanks in advance for any help!