Twist Per Inch Calculator

Twist per inch (TPI) governs how strong, elastic, and durable a handspun yarn will be, and how it must be spun is fiber- and style-dependent rather than a single universal number — which is why this calculator uses the twist-multiplier method instead of just the simpler "balanced yarn" rule of thumb. It first approximates the yarn's English cotton count (Ne) from your target WPI using a common woolen-spinning relation (WPI squared divided by 6.5), then multiplies the square root of that count by your chosen twist multiplier — a fiber- and style-dependent constant that's higher for woolen-spun wool (4.5-6.0, for loft and warmth) and lower for silk (2.5-3.5, for drape and sheen) — to get the calculated TPI. For comparison, it also reports the simpler √WPI "balanced yarn" rule of thumb, which is a reasonable default for medium-twist worsted singles but doesn't account for fiber type.

From the calculated TPI it derives an approximate twist (helix) angle in degrees using the yarn's estimated diameter, the plying twist needed to balance multiple singles (singles TPI divided by the square root of the ply count, since twist energy is distributed across the plies), and the total number of twists across one staple length of fiber — a sanity check where a result comfortably above 1 confirms the fiber has enough twist per staple to hold together during drafting. These are approximations rooted in classic handspinning formulas, not a physical model of your specific fiber's crimp or surface friction, so treat the outputs as a calibrated starting point to sample and adjust from at the wheel.