Guide · Glossary
Inventory planning glossary
The words fashion buyers use when they plan an order, in plain English: what each one means, how it’s worked out, and where it trips people up.
Published October 5, 2026 · By Sizo
- Allocation
- Censored demand
- Demand forecast
- Full-price sell-through
- Inventory distortion
- Lead time
- Lost revenue
- Markdown
- MOQ
- Open-to-buy
- Purchase order
- Reorder point
- Replenishment
- Safety stock
- Sell-through
- Size curve
- Size mix
- Size run
- SKU and variant
- Stockout
- Weeks of cover
- Allocation
- Deciding how many units of an order go to each shop and to the online store. Good allocation follows how fast each location sells each size, rather than splitting evenly.
- Censored demand also lost demand
- Demand you can’t see because the product was out of stock. Sales stop at what was on the shelf, so sold-out days look like zero demand, and the sizes that sell out fastest look weaker than they are.
- The fix is to measure sales per day in stock. See how, with a calculator.
- Demand forecast
- An estimate of how many units will sell in a coming period, by product, size and location. A forecast built on raw sales inherits censored demand and underestimates the sizes that keep selling out.
- Full-price sell-through
- The share of units sold before any markdown. When it is high, you bought close to what customers wanted, in the right sizes.
- Inventory distortion
- Stock in the wrong place, size or quantity: the combined cost of stockouts (sales you couldn’t make) and overstock (units left over or sold at a discount).
- Lead time
- The days between placing an order with a supplier and the stock arriving ready to sell. A reorder has to go out at least one lead time before the size runs out.
- Lost revenue from wrong orders
- What the free Sizo audit measures: sales missed because an order came too late or too small, plus stock sold at markdown because the wrong sizes were bought.
- Markdown
- A price reduction to clear stock. When the sizes left over are the ones you bought too many of, the markdown is a cost of the size mix, not of the product.
- Minimum order quantity MOQ
- The smallest order a supplier accepts, per style, color or whole order. Any split between sizes has to add up to at least the minimum.
- Open-to-buy OTB
- The budget left for purchases in a period. Planned sales, plus planned markdowns, plus the stock you want at the end of the period, minus the stock at the start, minus what is already on order.
- Purchase order PO
- The order you send a supplier: styles, colors, sizes, quantities, prices and delivery date. Sizo drafts it; you review it and send it.
- Reorder point
- The stock level at which to reorder: the sales you expect during the lead time, plus safety stock. Selling 4 a day with a 21-day lead time and 20 units of safety stock: reorder at 104.
- Replenishment restock
- Reordering a product that is already selling, as opposed to buying a new style. Restocks are where real demand can be measured, so they are where size data helps most.
- Safety stock
- Extra units held to cover demand that runs above forecast, or a supplier that delivers late.
- Sell-through rate
- Units sold divided by units received, or available, in a period, as a percentage. 80 sold out of 100 received is 80% sell-through.
- Size curve also size ratio
- The share of a product’s demand that falls on each size, for example S 20%, M 33%, L 33%, XL 13%. You use it to split an order between sizes. Built from raw sales it undercounts the sizes that sell out. Build a corrected one.
- Size mix
- The split between sizes in what you bought or hold. When the size mix you bought differs from the size curve customers want, some sizes sell out while others are left over; the cost of that gap is size-mix loss.
- Size run also size ladder
- The full set of sizes a style comes in, such as XS to XL or 36 to 44. A broken size run is one with sizes missing, which loses the customers who wear them.
- SKU and variant
- In Shopify, a variant is one version of a product, such as a color in a size. Each variant usually has its own SKU (stock keeping unit). Size planning happens at variant level.
- Stockout
- A size or product with no stock left to sell. The stockout rate is the share of products, sizes or days out of stock. How stockouts hide your best sizes.
- Weeks of cover also weeks of supply
- How long current stock lasts at the current rate of sale: units on hand divided by average weekly sales. 120 units selling 20 a week is 6 weeks of cover.
See these numbers for your own store
Sizo reads your Shopify data read-only and works them out for every product, size and shop. Start with a free audit of what wrong orders cost you over the last 12 months.