Things You'll Need
Don't worry if the rug pad is not exactly even when cut. The pad should work fine as long as it is placed beneath the center of the rug and the overhang on each side of the pad is roughly the same.
If you plan to put an area rug down on a flat floor, such as hardwood or tile, you should use an area rug pad. An area rug pad lies underneath the area rug, between the bottom of the rug and the floor's surface. The pad not only protects the surface of your floor, but also helps keep the rug from sliding around on the floor, which can prevent falls. Area rug pads often come larger than the rugs themselves, but you can cut an area rug pad down to size before placing it.
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Measure the rug that you plan to place the area rug pad under if you do not know the size. Take a measurement down both the length and across the width of the rug. Do not include any decorative ends, such as tassels, in the length measurement. Measure only the main part of the rug.
Subtract 2 inches from both the length and the width of the rug to get the measurements for the rug pad. Lay the rug pad out on the floor and measure the length that you determined for the pad down the side of the rug pad. Cut straight across the pad to cut a piece slightly shorter than the length of the carpet.
Measure the width measurement that you determined for the area rug pad across one end of the pad that you already cut for length. Cut the pad in the perpendicular direction so that it is the width you need.
Center the rug pad over the area of the floor where you want the area rug to lie. Lay the area rug over the rug pad so that roughly the same amount of the area rug hangs over the edges of the rug pad. This should be approximately 1 inch all around.