# How to Determine Load Bearing Capacity for Floors

By Heide Braley , last updated March 13, 2012
Before you move heavy objects into a room, you need to determine the load-bearing capacity of the floor, or you may stress it to the point of collapse. Generally, structures are built to hold a lot of weight; but if you are thinking of moving in a piano or maybe adding a large bathtub, you should check what kind of floor support is under the floorboards.
1. Look under the floor to determine what size floor joists is holding up the floorboards and how far apart the joists are spaced. You can check in the crawlspace or basement or possibly lift a few floorboards in a closet or corner. Measure the wood size to see if it is a 2-by-6 or a 2-by-8 then check the standards for load-bearing weights from a lumberyard's charts. To be very specific, you could also check on the wood type if you need more exact details for weight-bearing loads.
2. Use the lumberyard's chart to compare the size of wood joists with the amount of weight they can carry. A general rule is that typical 2-by-6 inch joists spaced 16 inches apart can hold 10 lbs. of dead weight per square foot or 30 lbs. of live weight. Live weight is moving, such as a person walking across the floor, whereas dead weight is stationary.
3. Calculate the dead weight load by multiplying the length of the floor joist by 10. For instance, a 12-foot-long joist can hold 120 pounds safely. If the item you want to move into the room spans several joists, multiply the dead weight allowance by the number of joists spanned.
4. Determine the total load-bearing capacity of the room by multiplying the number of floor joists by their dead weight capacity per square foot then multiply that answer by the length of the joists. For example, a typical 2-by-6 floor joist set 16 inches apart in a 12-foot square room can hold 10 pounds of dead weight per foot, so nine joists that hold 90 pounds multiplied by the length of the 12-foot joist equal 1,080 pounds.
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