The provided context is very limited and does not contain specific instructions on how to measure a sofa spring, though it does identify zig-zag (also known as no-sag or sinuous) springs as a common type. Based on general upholstery expertise, the measurement process depends on the type of spring you are replacing.
For sinuous or zig-zag springs, the most accurate method is to measure an existing, unbroken spring from the same piece of furniture. Remove the spring, lay it flat, and measure its overall length from end to end. If you do not have an intact spring to use as a reference, measure the distance between the mounting clips on the inside of the sofa's frame. The new spring must be slightly longer than this distance to create the necessary tension and upward arch, or "crown." A common practice is to order a spring that is one to two inches longer than the frame measurement.
If you are measuring coil springs, you will need to take several measurements to find a suitable replacement. First, measure the height of the spring from its top loop to its bottom loop. Next, measure the diameter of the top coil. You should also count the number of turns or loops in the spring. Finally, it is important to identify the gauge, or thickness, of the spring wire, as this determines its firmness. A lower gauge number signifies a thicker, more supportive spring. Taking these precise measurements is essential for restoring the proper feel and support to your sofa.
