What size tarp do you need to cover 17'X13'X70?

To cover an area of 17' x 13' x 70', you need to first determine the total surface area you want to cover. If you are covering just the top, you would need a tarp that is at least 17' by 70', plus a bit of extra for overlap and securing. Therefore, a tarp measuring 18' x 72' would be a good choice to ensure complete coverage.