Size Run Calculator

This calculator splits a production run across your size range using a Gaussian (bell curve) distribution centered on whichever size you designate as the peak seller — almost always a middle size like Medium. Each size's share of the total is weighted by exp(−distance² / (2σ²)), where distance is how many size-positions that size sits from the peak; sizes right at the peak get the full weight while sizes further away taper off following the classic bell-curve shape. The curve's steepness is controlled by the spread setting: "Tight" uses a narrow σ of 0.8, concentrating units heavily on the peak size and its immediate neighbors; "Wide" uses σ = 2.0, spreading units more evenly across the whole range; "Normal" sits in between at σ = 1.2.

All size weights are normalized to sum to 1, then multiplied by total units and rounded to whole garments — since rounding several sizes independently can leave the total off by a few units, any rounding difference is added back onto the peak size specifically, so the sizes that matter least aren't the ones absorbing the adjustment. The result is a size-by-size allocation plus the peak size's unit count and the smallest size's unit count for quick reference. This model assumes your actual sell-through genuinely follows a bell curve around one peak size — it won't fit bimodal size distributions (common when a style skews toward both petite and plus customers) or brands whose best-selling size sits at an extreme rather than the middle, so validate the peak position and spread against your own sales history before committing a full production run to it.