how to calculate how much underlay i need?
["Fill in the boxes labelled 'Length' and 'Width' for each room or area required.", 'Only use numbers.', 'Enter all figures in Metres, like the example below – (There are 15 sq meters on a roll.)', 'Calculate as many rooms as you like.', 'When estimating for stairs, a rough guide is that 12 stairs requires 3m by 0.90m.']