Draw a rough floor plan of the room in which you plan to install the carpet pad. Be sure to include any obstructions or odd shapes in the floor plan of room that will affect where you will place the carpet pad.
Measure the length of each wall in the room using a measuring tape. Note the dimensions on the floor plan.
Determine the area of the room by multiplying the width by the length using a calculator. This basic formula will work if your room is a rectangle or square. If your room is not a rectangle or square, skip this step.
Break up an irregularly shaped room into basic shapes using dotted lines on the floor plan. Calculate the area of each shape, and then add the areas together for the total square footage. For right triangles, multiply the height of the triangle by the base measurement of the triangle and then divide that number in half.
Order rolls of carpet pad using the square footage of the room. Most carpet pads are available in 6-foot-wide rolls. To find out the square footage of a roll of carpet padding, multiple the length of the roll by 6.
Purchase the roll closest to the square footage of the room. Most manufacturers recommend allowing for a 5 percent variance when purchasing rolls of carpet padding, so make sure that the square footage of your room is only 95 percent of the square footage of the carpet pad. To verify the percentage, divide the room's square footage by the roll's square footage. If the result is .95 or lower, that roll is suitable for the room.
Things You Will Need
- Measuring tape
- Never use the square footage required for carpet pads to order carpet. Most carpets require some matching. Even if there is no repetitive pattern, you should you order 10 percent more than you think you'll need.
- To ensure your measurements are accurate, ask someone to assist you to measure the room.