There is no hard and fast rule for converting pounds per linear foot to pounds per square foot because there is no rule to convert from linear feet to square feet. To convert from linear feet to square feet, you need to know the width, because square feet is calculated by multiplying the length times the width. Pounds per square foot is used to measure pressure, such as the pressure of a gas inside a balloon.
Multiply the number of pounds per linear foot by the number of linear feet to determine the total number of pounds. For example, if your pounds per linear feet is four and you have six linear feet, multiply six times four and get 24 pounds.
Determine the width that you will be using to convert linear feet to square feet. For example, if you are using a platform that is six linear feet long and eight linear feet wide, you would use eight for the width.
Calculate the number of square feet by multiplying the number of linear feet by the width. Continuing the example above, you would multiply six times eight to get 48 square feet.
Divide the number of pounds the square feet will be subjected to by the number of square feet. For example, if you are putting 24 pounds on the 48 square foot platform, you would divide 24 by 48 and find that you have 0.5 pounds per square foot.