Based on the provided search results, there is insufficient information to detail the process of measuring a sofa pillow. The context consists primarily of website navigation links and metadata rather than instructional content. Therefore, the following answer is based on general knowledge of the subject.
The standard and most accurate method for determining the size of a sofa pillow involves measuring the pillow cover when it is empty and laid flat. Industry sizing conventions are based on these flat dimensions, not the dimensions of the pillow once it is filled. To perform this measurement, remove the insert and place the cover on a flat surface. Using a firm or metal measuring tape, measure the distance from one interior seam to the opposite interior seam. This should be done for both the length and the width to ascertain the pillow's official size, for example, 18 x 18 inches.
If you are measuring a pillow that already has an insert inside and cannot be removed, the process requires a slightly different approach to account for the loft, or fullness, of the pillow. Measuring directly across the domed center of a stuffed pillow will result in an inaccurate and smaller measurement. The correct technique is to measure along the seam or cording. Place the pillow on a flat surface and use a flexible measuring tape. Hold the end of the tape at one corner and follow the edge of the pillow along the seam to the opposite corner. Pull the fabric slightly taut to get the most accurate reading. Repeat this for the other dimension. This seam-to-seam measurement provides the closest approximation to the pillow cover's true flat dimensions.
