How to calculate market share?

In large retail, calculating your market share is essential for understanding your positioning, steering your commercial performance, and adjusting your strategy. This indicator allows you to measure the place your brand occupies, your products, or your company relative to the entire market, in volume or in value.

But how do you calculate this market share? What data should you use? And above all, how do you interpret it as part of your commercial actions?

‍In this article, we explain step-by-step how to calculate a market share, with concrete examples, simple formulas, and the most common use cases in large food supermarkets (GMS).

How to calculate market share in 3 steps

1. Define the reference market: the category, geographical area, and period.

2. Collect two figures: your sales and total market sales, in volume (units, liters) or in value (turnover).

3. Apply the formula: divide your sales by total market sales, then multiply by 100.

The different ways to calculate market share

There are two ways to calculate market share: in sales volume or in turnover, depending on your commercial objective or negotiating needs.

Market share by volume

The goal is to measure the quantity sold relative to the total market. For example:

• A beer brand sells 10,000 L.

• The total draft beer market = 100,000 L.

➡ Volume market share = (10,000 ÷ 100,000) × 100 = 10%.

Market share by value

The goal is to measure the value of sales relative to the market. For example:

• A beer brand has a turnover of €50,000.

• The total market turnover amounts to €500,000.

➡ Value market share = (50,000 ÷ 500,000) × 100 = 10%.

Relative market share

Relative market share compares your brand not to the entire market, but to your main competitor (often the leader).

For example: your brand holds 15% of the category, the leader holds 30%.

➡ Relative market share = 15 ÷ 30 = 0.5

You carry half the weight of the leader. A result greater than 1 means you are the leader. This is the axis of the BCG matrix.

Market share in large retail (GMS)

Market share (MS) is calculated by comparing the sales of a product or brand to the total sales of the category. In large retail, its calculation is often based on panel data (Nielsen, Kantar, Circana), which provide retailers with an agnostic view of the market.

Market share and assortment

Market share remains a central criterion for retailers when they build an assortment.

‍If a category represents 25% of an aisle's sales, it tends to occupy about 25% of the assortment. Within this category, each brand has its relative weight reflected by its market share.

‍For example, if tomato sauce accounts for 10% of the "savory grocery" aisle, it will represent about 10% of the offering. And if a brand holds 15% of the market share for tomato sauce, it will occupy an equivalent space on the shelf.

👉 Discover how to optimize your product assortments in large retail.

Market share and sell-in

Beware: market share alone is not enough.

Two important nuances to recall:

1. High market share ≠ necessarily high turnover: a category may weigh heavily in market share but be positioned at low prices. Conversely, a premium category, though smaller in volume, can generate a higher turnover. This explains why retailers also make decisions based on potential turnover, and not just market weight.

2. Market share differs by territory and consumption type: what works in Lille does not necessarily reflect the reality in Marseille. Retailers, thanks to panelists (Circana, NielsenIQ, Kantar…), analyze these differences to adapt assortments locally. That is the whole purpose of store clustering: calibrating the offer according to the consumption profile of an area.

How to estimate market share without complete panel data?

Many brands, particularly SMEs or those starting out in large retail, do not have access to Circana or NielsenIQ panels. Without this data, calculating market share to the exact figure becomes impossible, but it is still possible to estimate it reliably using three methods.

1. The top-down method: starting from the market size

This approach is suitable when you know your own sales well, but not the details of the market. The first step consists of finding the total size of the market from external sources: sector studies, professional federations, Xerfi or INSEE publications, or public reports from Circana and NielsenIQ. Then, simply divide your sales (in volume or value) by this total, and multiply by 100.

Example: if your brand generates €200,000 in turnover in a market estimated at €4 million, your market share is around 5%.

2. The bottom-up method: starting from the field

This approach is useful when the market size is neither known nor published. The idea is to reconstruct an estimation from your own field data. In practice: on a representative sample of stores that you monitor, collect your sales as well as the total sales of the category (checkout scanner data, numeric distribution, and value). You thus obtain your real market share on this sample, which you can then extrapolate to your entire area.

The advantage: this estimation reflects a local reality, often more actionable for a sales representative than a national average from a panel.

3. The survey or proxy method

When your market is too specific to be tracked by panels, two solutions exist. The first is to use a broader category as a reference: for example, estimating your share in "organic snacks" using available data for "snacks" as a whole. The second relies on a consumer survey (awareness, frequency, and volume of purchase) whose answers are then converted into an estimated market share.

To keep in mind: an estimation is only as good as the rigor of its assumptions. Always specify the scope chosen (category, geographical area, period) and indicate the source of each figure: this is what distinguishes a defensible estimate from approximate data.

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