Retail Dogma

Size Curve : Definition, Planning & Factors

What is a Size Curve?

A size curve represents the distribution of quantities of different sizes in the size run a retailer is carrying inventory for. It is a relationship expressed in relative numbers.

For example, 1:2:2:1 would mean that for each 1 piece of the first size 2 pieces of the second and third sizes and 1 piece of the fourth size are carried.

So if you are ordering 60 pieces of a product that has a size run from Small to X-large, your order will look like this:


Read More On: Size Run

Size Curve Analysis & Planning

How to determine the size curve for your products?

When you are just starting out in your fashion business and don’t have any historic sales data, you will usually go for a normal distribution size curve.

This curve (see below) resembles a normal bell shaped curve, where the middle sizes are sold and carried in higher quantities and extreme (small or large) sizes are sold and carried in smaller quantities.

Normal Size Curve
Normal Distribution Size Curve

After you start trading and start collecting data about sales by size, you will then analyze the sell-through rates for each size and see which ones are selling out faster and which ones are remaining behind until the end of the season.


You will then start to plot down your own size curve, which might start to look much different from the initial normal distribution size curve.

Remember while doing the size curve analysis to account for missed sales opportunities. If a size sells out early on after the season’s launch, it means that it could have sold more pieces if more was carried. When you do your analysis and plan for future purchases, take this into consideration.

Skewed Size Curve
Skewed Size Curve

Your size curve could now be skewed towards bigger or smaller sizes, depending on many factors that affect size curve distribution.

Which takes us to the next point…

Factors Affecting Size Curve Distribution

There are many factors that play a role in how you will plan the size curve of your collections.

Customer Demographics

The main factor affecting size distribution is the customer profile and demographics your store is serving.

We have operated different stores for the same brand, where one store would have a totally different size distribution than the other.

For example, we run a store in an area dominated by customers from Asian origins. The size distribution for this store was more skewed towards smaller sizes, and so we had to take this into consideration while buying and merchandising for this store.


Another factor that could affect the size distribution for your store is whether or not your competition are catering for specific size ranges.

For example, we have run an ecommerce store with a specific section for big sizes (XXL, XXXL,..etc). Because these sizes were not catered for by other retailers in the area or other ecommerce businesses they tended to sell fast at our website.

Some retail businesses, especially big ones, find it unfeasible to cater for extreme sizes. In this case, when a small player carries these sizes they tend to sell faster, not because the demographics of the market reflect this, but rather due to the lack of competition.


Not all suppliers will give you a free hand in choosing your own size curve, and so you will have to adopt their own size distribution if you want to carry their products.

Read more on: The Bargaining Power of Suppliers

This is because they want to make sure they manufacture and sell the full size run evenly and not have to bother about leftovers that they have to clear at a discount.

If you are dealing directly with manufacturers, you will be able to dictate your sizes. If, however; you are dealing with wholesalers or distributors, chances are, you will have to adopt their distribution and then clear out the unsold sizes at the end of the season from your stores.

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More Resources

Thank you for reading this article on Size Curve. We recommend the below free resources as well:

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