Size Curve vs Size Ratio: How To Choose The Right Mix

The distribution of sizes expected or ordered for a particular apparel style, market, or customer segment.

Size Curve

The distribution of sizes expected or ordered for a particular apparel style, market, or customer segment. In practice, teams often compare size curves to related concepts like size ratios and pack ratios to decide which approach fits their supply chain and selling channels.

Planners and buyers use the terms size curve and size ratio interchangeably at times, but there are operational differences that affect ordering, production, and fulfillment. A size curve is typically a dynamic distribution expressed as percentages across sizes for a style and market; a size ratio or pack ratio can be a fixed multi-pack or a factory cut order. Understanding the difference helps you choose the right method for the right stage of the product lifecycle.

Key Differences

• Expression: Size curves are usually percentages (e.g., M 35%); size ratios are often integer ratios used for cartons or cut packs (e.g., 2:3:3:2 for S:M:L:XL).
• Flexibility: Curves are adjusted frequently based on sales data; ratios are sometimes locked in for production or cartonization constraints.
• Application: Curves inform buying and replenishment. Ratios dictate what factories cut and how carton packs are assembled for shipping.

When To Use A Size Curve

Use a size curve when you need flexibility to respond to sales patterns or when you maintain central inventory and allocate to channels. Curves are ideal for:

• Initial Buys: Translating forecasted units into size-level buys while allowing later adjustments.
• Replenishment Planning: Feeding allocation engines that distribute inventory by store or region.
• Data-Driven Reordering: Where frequent updates are possible and desired.

When To Use A Size Ratio

Use fixed ratios when manufacturing, shipping, or retail packaging requires consistent pack structures. Typical use cases include:

• Factory Cut Orders: Cut-to-pack or cut-to-size operations often require integer quantities matching cutting tables.
• Case Packs: Retailers or distributors that receive sealed cartons with a fixed size mix demand explicit ratios.
• Wholesale Orders: Large B2B orders where buyers expect standard pack units for ease of counting and display.

Operational Implications For Warehouses And 3PLs

Choice of curve vs. ratio changes packing, slotting, and return flows. If product arrives in fixed case packs, warehouses configure picking and replenishment to those pack sizes. If inventory is allocated by curve and arrives loose, the WMS must support dynamic pick densities and frequent replenishment. Misalignment can cause over-handling or increased labor.

• Slotting: Fixed ratios simplify slotting because SKU-case quantities are predictable.
• Pick Efficiency: Loose sizes picked to order require more complex pick profiles if demand is skewed.
• Returns Processing: Size mismatches can complicate restocking if returned units don’t match expected pack ratios.

How To Choose The Right Approach

Decision factors include supply chain flexibility, production constraints, and channel mix. A pragmatic approach combines both: use curves for planning and ratios for execution when necessary. For example, set a curve for the season but translate that into production ratios for the initial factory order, keeping a portion of inventory flexible for later replenishment runs.

• Start With Data: Use sell-through and returns to define a baseline curve.
• Test Pack Ratios: Run small production batches with different ratios to validate demand assumptions.
• Maintain Flexibility: Negotiate smaller minimum runs or mid-season cuts with suppliers when possible.
• Align Systems: Ensure ERP/WMS can map planned curves into packed case ratios and support replenishment adjustments.

In short, the Size Curve is the demand-focused distribution you should use for planning. Size ratios are the execution tool used at production and packing. Use curves to guide decisions and ratios to meet manufacturing and shipping constraints, and reconcile the two with staged buys and responsive replenishment.