The Meat and Potatoes of Volume Effect

 Volume effect is the second piece of the revenue bridge puzzle. (The first being the price effect from the last post) Why do we need to measure it? Because price changes often influence volume — and so do many other market factors. Economic theory suggests that price and volume are closely linked. To truly understand their impact on revenue, we need to isolate and measure each effect independently — first, how price changes influence revenue, and then how volume shifts contribute. While these factors are often analyzed together, separating them allows us to see how each one drives revenue on its own.

A powerful historical example of volume change comes from the Irish Potato Famine 🥔 in the mid-1800s. Due to a devastating fungal disease known as potato blight, potato crops across Europe failed. In Ireland, it’s estimated that 30–50% of the crop failed in 1845, and by 1846, that number rose to 75%. The country went from producing nearly 4 million tons of potatoes per year to just 1 million tons — a staggering drop, enough to feed millions. It wasn’t just the change in volume that made this event so catastrophic — it was the suddenness of that change.

Thankfully, most businesses won’t face volume shifts that dramatic. But even small changes in volume — whether gradual or sharp — can be measured using the volume effect. Here’s how it works:

  1. Sum the quantity sold in the base period.
  2. Sum the quantity sold in the current period.
  3. Calculate the difference between the two.
  4. Multiply that difference by the ASP (Average Selling Price) from the base period.

Let’s bring this to life with a simple example:

  • Base Period: Customer 1 buys 100 units of Widget A at $10 → $1,000 revenue → ASP = $10
  • Current Period: Customer 1 buys 110 units at $11 → $1,210 revenue → ASP = $11
  • Volume Effect: (110 - 100) × $10 = $100 uplift

The increase in quantity alone — independent of price — contributed $100 in additional revenue. This graph illustrates a clear and distinct measure of how volume alone has impacted revenue.

Generated Image

Below, you’ll see a graph using the same example from last week — but this time I’ve added both price and volume effects, helping illustrate how each component contributes to the overall revenue bridge.

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 The revenue bridge is beginning to take shape — one effect at a time. More on mix effect, FX effect, and subgroups of volume to come. 

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