Inventory glossary
What is Demand variability?
Demand variability is how much a product's sales move up and down from one period to the next instead of following a steady, predictable pattern.
If a product sells roughly the same amount every week, you can plan stock close to the bone. If it swings wildly between busy and slow weeks, you need extra buffer because a single bad guess can mean a stockout or a pile of unsold stock. Knowing which of your SKUs are steady and which are jumpy tells you where to focus attention.
In practice, use it to decide how much safety stock to carry per SKU. Steady sellers need little cushion. Volatile ones, like a seasonal candle scent or a trend-driven apparel print, need more buffer stock or shorter, more frequent reorders so you are not stuck guessing months ahead.
Formula
Example
A candle shop sells a lavender candle in weekly amounts of 20, 22, 19, and 21 units. Average is 20.5, and the numbers barely move, so demand variability is low. The same shop sells a pumpkin spice candle at 5, 40, 10, and 60 units over four weeks. Average is also around 29, but the swings are huge, so demand variability is high and that candle needs a bigger safety buffer.
Common mistakes
- Treating all SKUs the same when ordering, instead of giving volatile ones more buffer.
- Looking only at average sales and ignoring how much actual weeks differ from that average.
- Confusing variability with seasonality, when a product can be seasonal and still fairly predictable within each season.
Demand variability and SteadyShelf
SteadyShelf's forecasts account for how erratic a SKU's past sales have been, so reorder suggestions and order-by dates are more cautious for unpredictable products and tighter for steady ones.
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Related terms
Safety stock · Demand forecasting · Service level · Z-score in inventory · Seasonality
FAQ
Why does demand variability matter more than average sales alone?
Because two products can have the same average sales but very different risk. A steady seller needs little safety stock, while a volatile one can stock out or pile up unsold units even with the same average, so you need extra buffer to cover the swings.
How does demand variability affect safety stock?
Higher demand variability means you need more safety stock to avoid stockouts, because sales in any given period can land far above or below the average. Low variability lets you carry less buffer and still stay covered.
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