Upholstery Spring Calculator

Coil springs and sinuous (zig-zag) springs are laid out completely differently, and this calculator switches its math depending on which one you pick. For 4" or 6" coil springs, it builds a grid: usable width and depth (frame dimensions minus the edge setback on both sides) are each divided by your spring spacing to get columns and rows, and total spring count is rows times columns — a true two-dimensional layout, since coil springs need support across the whole seat area. Sinuous springs instead run as continuous strips from front to back, so only one dimension (usable width divided by spacing) matters; each strip counts as one "spring" in the totals. Recommended spring height assumes coil springs compress to about 60% of their free height under a seated load, so free height is set relative to your target cushion thickness (at least the coil's own gauge height of 4" or 6").

Spring gauge recommendations shift toward a firmer wire (lower gauge number, since gauge numbering is inverted) as cushion height increases, favoring firmer support for thicker, softer-feeling cushions. The fabric yardage estimate is built from four separate pieces — seat deck, cushion cover (top, bottom, and boxing per cushion), inside back, and outside back — each with its own margin allowance, summed and then padded 15% for cutting waste and pattern matching, assuming standard 54"-wide upholstery fabric. Twine length is calculated only for coil springs, since sinuous springs are clipped rather than hand-tied in a traditional 8-way pattern.