How much extra carpet underlay do I need?

cybervic

I need 57.5m2 of carpet underlay (measured 3 times). Most online shops recommend to buy 10% extra. This makes it 63m2 which mean I will have to buy an extra roll (Each roll is 15m2) or carpet underlay that I may not need?  Anyone knows if I'll be alright with buying just 4 rolls (60m2)? Do I really need to buy 10% extra of underlay?

Thanks.

grumbler

What sort of underlay? I think you can connect smallish pieces with duct tape underneath - thus avoiding any losses and getting very close to 0% extra.

Gastines3

very unusual to use the same amount of underlay as carpet. Just look at any cut-outs required/fireplace/bay-window etc. Stores estimating the same amount of underlay as carpet was the best way of making an extra profit of short rolls and cut-outs being used on the next job.

FaceHead

Yes - go with 60msq (that's 4% wastage) and you'll be fine.

You can get away with only marginally more underlay than the floor are to be carpeted as you can use your offcuts in odd corners. It doesn't matter if the underlay is in two pieces across the room or a window bay in the way it would be unacceptable to have a cut across the carpet in the middle of the room.

cybervic

I'm buying connoisseur 10mm. Thanks so much for the input.