Size Curve Planning: How Many of Each Size to Buy
Your size curve is how many units of each size you buy. Get it wrong and you sell out of mediums in a week while XXLs sit for a year — tying up the cash you needed for the reorder.
Quick answers
- What is a size curve?
- How your buy is split across sizes
- Where does demand peak?
- Usually the middle sizes (M/L)
- Biggest planning mistake?
- Reading sold units without checking stock-outs
- Should I drop slow sizes?
- Rarely — dropping them alienates customers
A Typical Size Curve (Illustrative)
| Size | Share of buy | Note |
|---|---|---|
| XS | ~5–10% | Thin tail |
| S | ~20% | Building |
| M | ~30% | Peak |
| L | ~25% | Peak-adjacent |
| XL | ~10–15% | Tapering |
| XXL | ~5–10% | Thin tail |
Notes
The curve in this table is a starting point, not your answer. Real curves differ enormously by brand, category, and customer. Use a bell-shaped default for your very first buy, then replace it with your own sales data as fast as you can. Anyone who tells you there's one universal curve is selling something.
Stock-outs lie to you. If mediums sell out in week one, medium's recorded sales are capped by supply, not demand. Plan the next buy from that number and you'll under-buy mediums again — forever. Always adjust for how long each size was actually available.
Don't quietly drop the tails. It's tempting to stop buying XS and XXL because they turn slowly. But dropping sizes you advertise alienates exactly the customers who struggle most to find their fit — and who become loyal when you serve them. Buy fewer, not none.
Good sizing makes the curve more predictable. When shoppers know their size in your brand, they buy one and keep it, and your sales data becomes a clean demand signal. When they're guessing and bracketing, your size mix is polluted with orders that were always going to come back.
FAQs
What is a size curve in retail?
The distribution of how many units you buy in each size. Demand typically peaks in the middle sizes and tapers at the extremes, but the exact shape varies enormously by brand and category — use a bell-shaped default only for your very first buy.
How do I know how many of each size to order?
Use your own sales history, adjusted for stock-outs. A size that sold out early has its demand understated, so planning from raw units sold will make you under-buy it again. Correct for how long each size was actually available.
Should I stop stocking sizes that sell slowly?
Usually buy fewer rather than dropping them. Cutting sizes you advertise alienates the customers who have the hardest time finding their fit — and who become your most loyal buyers when you do serve them.
Need this on your store?
Tailor Size Guide ships pre-built size charts for Shopify.