Size Curve Planning for Custom Runs
10 Customization & Manufacturing
Size curve planning replaces an even split with the quantities buyers order. A bulk run divided equally across six sizes looks fair and produces leftovers in the extremes while the middle sizes sell out in a fortnight. Size curve planning uses historical orders by market to weight each size, so the run leaves stock where demand sits and reduces the orphan sizes that end up discounted.
The curve is a planning input, not a forecast. It tells you how to divide a fixed quantity, and it needs revisiting whenever a market, a product or a season changes. A curve built on last year's data for a different silhouette will miss, and a curve never reviewed will drift into the same even split it replaced. Two numbers per style are enough to start, and both come from orders you already have.
Why an even split fails
Demand is not flat across a size range. Most apparel ranges sell a disproportionate share in the middle sizes and a smaller share at both ends, and the shape of that distribution changes by category. A fitted dress, an oversized hoodie and a children's tee each produce a different profile. Splitting a run evenly means the middle sizes run out while the extremes sit in storage, and storage is where margin goes to die.
The cost is not only the unsold units. A stockout in a middle size loses the order and often the customer, because a buyer who cannot find their size in one style rarely tries the next. Size curve planning protects the sizes that carry the revenue and treats the tail as a deliberate, smaller allocation rather than an equal share of the risk.
Building a curve from order data
Size curve planning starts with twelve months of orders for a comparable product and group sales by size. Convert the counts into percentages rather than units, so the curve can be applied to any run quantity later. A range that sells 4 per cent in the smallest size, 12 per cent in a small, 26 per cent in a medium and so on gives you a distribution you can multiply by any order quantity.
Round the result to whole units and correct the total so it matches the run. Rounding up each size individually inflates the order, and rounding everything down leaves you short of the minimum. Adjust the largest size band for the residual, and check the result against the grading rules that govern how a pattern scales between sizes, which the notes on pattern grading and size runs set out for cut and sew production.
How market changes the size curve
Size distribution varies by country more than most sellers expect. Averages shift, the share of the largest sizes rises or falls, and the length of the grading run changes with the market. Building one curve for all markets and applying it everywhere guarantees that some regions receive the wrong mix, so keep a separate curve per market once a product has sold in more than one.
Extended sizes need their own decision. Including them widens the range and serves buyers who are poorly served elsewhere, and the approach in the notes on plus size apparel in print on demand shows how to add them without turning the tail into dead stock. A small opening allocation tested on one style tells you more than a full commitment across a range.
Size curve planning for bulk runs
Bulk runs magnify every error in size curve planning. A curve that is 5 per cent wrong across a hundred units is a rounding problem, and across five thousand units it is a warehouse full of the wrong size. Weight the curve toward the sizes that carry revenue, hold a small reserve of the middle bands, and resist the temptation to raise the extremes to fill a supplier minimum.
Decide the inventory model before the size curve planning step. A brand that restocks quickly can run a tighter curve and take the risk of a stockout, while one that orders once a season has to hold more of the tail. The comparison in the guide to POD and bulk inventory explains where that break-even sits for print on demand sellers.
Timing the run against the curve
Size curve planning only helps if the stock arrives before the demand. Work back from the selling window, add the production and transit lead time, and set the order date from that calculation rather than from a supplier's preferred schedule. Peak windows compress, and the cutoff points in the notes on Cyber Monday fulfillment cutoff apply to any high-volume period, not only one holiday.
Seasonality reshapes size curve planning as well as the calendar. A gifting period skews toward the middle and larger sizes for adult products and blurs the profile for children's items, and the pattern in the guide to seasonality planning shows how to shift allocation without overcommitting. Review the curve after every run, because size curve planning improves with each cycle of evidence. CatKissFish ships from a US warehouse and produces 90% of orders in 2 to 3 days, which shortens the feedback loop between a run and the data that should shape the next one. Browse the custom product catalogue and start your custom order today.
