What is Theoretical Usage?
Theoretical usage is how much of a product you should have used in a period, based on what you sold and the recipe for each item.
It's the "should" side of inventory. Your counts tell you what actually left the shelf; theoretical usage tells you what should have. The gap between them is your Inventory Variance.
The Formula
For each product:
Σ (Units Sold × Amount per Recipe) = Theoretical Usage
Add up every menu item that uses the product. Multiply by cost per ounce to get theoretical cost. Divide total theoretical cost by sales to get theoretical Pour Cost.
Quick Example
One week of vodka:
Vodka Soda: 100 sold × 1.5 oz = 150 oz
Espresso Martini: 30 sold × 2 oz = 60 oz
Theoretical usage: 210 oz (about 8.3 bottles at 750 ml)
If your counts show you actually went through 9 bottles (228.2 oz), you have 18.2 oz unaccounted for. That's an 8.7% variance, worked through on the Inventory Variance page.
Why It Matters
It's the baseline for variance. Without it, an inventory count tells you what you have, not whether anything went wrong.
It shows what your pour cost should be if every drink is made to spec.
It helps with ordering. If you know how much a week of sales uses, you can set Par Levels from data instead of instinct.
What You Need to Calculate It
Accurate recipes. Every drink's spec, with exact amounts of every ingredient.
Sales by item. Your POS product mix report.
A match between the two. Every POS button needs to map to a recipe, including modifiers.
Sub-recipes broken down. If vodka goes into a batched Espresso Martini, theoretical usage has to follow it through the batch to the bottle. See Recipe Costing.
Common Mistakes
Specs that don't match the bar If the recipe says 1.5 oz and the bar standard is 2 oz, theoretical usage will always run low, and variance will look worse than it is.
Ignoring modifiers "Make it a double," "upgrade to Tito's," and "extra shot" all change usage. If the POS doesn't ring them, theoretical usage misses them.
Losing products inside batches Spirits in a pre-batch, syrups with sugar, and infusions all need to be traced back to the base product.
Forgetting what doesn't get rung in Comps, staff drinks, and spillage don't show up in sales. That's fine, but know that they'll show up as variance.
Treating it as actual cost Theoretical usage assumes perfect execution. It's a target to measure against, not what you actually spent.
Theoretical vs Actual Usage
Theoretical usage = what you should have used, from sales and recipes
Actual usage = what you did use, from inventory counts: Beginning Inventory + Purchases − Ending Inventory
Actual minus theoretical is your Inventory Variance. The same comparison in dollars is the gap between your actual and theoretical pour cost; see Weighted Pour Cost.
FAQ
What's the difference between theoretical and actual usage? Theoretical usage comes from what you sold. Actual usage comes from what you counted. The gap between them is variance.
Does theoretical usage include waste? No. It assumes every drink was made exactly to spec and every pour was rung in. Waste, spills, and comps show up in variance.
Why calculate it if I already count inventory? A count tells you what's on the shelf. Theoretical usage tells you what should be on the shelf. You need both to know if anything is going wrong.
Do I need to do this for every product? Start with liquor and your highest-volume items. That's where most of the money is.
Do This in Spec
Theoretical usage depends on exact recipes. Spec stores every recipe and sub-recipe with exact amounts, so batches and house-made ingredients trace back to the products they use.
Related Terms
Related Guides from Spec
Bottom Line
Theoretical usage is your recipe book turned into a number. It's only as good as your specs, so keep them accurate, and it becomes the yardstick every inventory count is measured against.
