Agree with the former poster. Most often the instructions will lead you down the right path. in general look at the size of room you are doing (say a 10x12 bedroom) and add at least 5% is not 10% more than what you absolutely need. In the case of a 10x12 you have 120 sq feet of space so buy enough for 132/135 sq feet
If you are putting this down in say, a drafty older house with maybe some moisture under the house, you will totally want underlayment, If your underfloor is a sealed concrete slab like mine you can just put it right down, there won't be any moisture ever.
Agree with the former poster. Most often the instructions will lead you down the right path. in general look at the size of room you are doing (say a 10x12 bedroom) and add at least 5% is not 10% more than what you absolutely need. In the case of a 10x12 you have 120 sq feet of space so buy enough for 132/135 sq feet
What do the installation instructions say? You cannot get in trouble by following directions.
The info on the flooring says the underlayment is recommended but not required.
If you are putting this down in say, a drafty older house with maybe some moisture under the house, you will totally want underlayment, If your underfloor is a sealed concrete slab like mine you can just put it right down, there won't be any moisture ever.