Drafting Ratio Calculator

The drafting (draw) ratio tells you how many times thinner your singles must be pulled out from the starting roving to hit a target yarn weight — a number that matters because getting it wrong is the single most common reason handspun yarn comes out thicker or thinner than planned. This calculator starts from your target finished yarn's WPI (wraps per inch) and applies McMorran's balance (yards per pound = your WPI value multiplied by itself and scaled up by 100, with that result split evenly across the ply count) to get the finished yarn's yards per pound. Since each single is thinner than the plied yarn it becomes, the required singles yards-per-pound is that figure multiplied back out by the ply count.

Dividing singles yards per pound by your roving's yards per pound gives the total draft ratio — literally the fold-change in grist from input to output. For multi-zone industrial drafting frames, the total draft is distributed evenly across zones as the total ratio's Nth root, where N is the zone count; this is only meaningful for a wheel or frame with actual staged drafting zones, and hand spinners on a single wheel should treat total draft as the whole story. A recommended technique is offered based on how aggressive the ratio is: low ratios suit a short forward draft, moderate ratios a standard worsted draw, and high ratios call for long draw or even pre-drafting the roving by hand before it reaches the wheel, since very high single-pass drafts get difficult to control smoothly.