Inventory Turnover Calculator

The arithmetic

Inventory turnover is cost of goods sold divided by average inventory value, and it counts how many times the stock is sold and replaced in a year. Using COGS rather than revenue matters, dividing revenue by inventory at cost inflates the ratio by the whole gross margin.

Average inventory is normally (opening + closing) ÷ 2, though for a seasonal business a twelve-month average is far more honest, because opening and closing figures are usually taken at the quietest point of the year.

Numbers on it

The example product sells 2,080 units a year at $18 cost, so COGS is $37,440. With an EOQ of 280 the average cycle stock is 140, plus 34 of safety stock: 174 units, or $3,132 of average inventory.

Turnover is 37,440 ÷ 3,132 = 11.95 times a year. Days sales of inventory is 365 ÷ 11.95 = 30.5 days.

The revenue error for comparison: 2,080 × $58 = $120,640 divided by $3,132 gives 38.5, which is not a turnover figure at all; it is turnover times the price-to-cost ratio, and it makes every business using it look three times better than it is.

What it does not tell you

A high turnover can mean efficient stock management or chronic understocking, and the ratio cannot tell them apart. A business turning stock twenty times a year while stocking out weekly is losing more in unmet demand than it saves in carrying cost.

Aggregate turnover also hides everything. A business turning stock at 12 overall may have half its capital in items turning at 2 and the rest in items turning at 40, and the average describes neither group.

What follows from it

Calculate it per SKU, not for the business. The aggregate figure is a reporting number; the per-SKU figures are where the decisions are: which products to reorder, which to mark down, which to drop.

Then look at turnover alongside gross margin rather than alone. A product turning 4 times at 60% margin generates more return on the space it occupies than one turning 12 times at 15%, which is precisely what GMROI measures and turnover alone cannot see.

What good turnover looks like by category

Benchmarks vary enormously and comparing across categories is meaningless. Grocery and fresh food commonly turn 15 to 25 times a year. General ecommerce and consumer goods run 6 to 12. Apparel is typically 4 to 6, jewellery and furniture 1 to 3, and heavy equipment lower still.

The pattern is that turnover falls as unit value and selection breadth rise, which is arithmetic rather than performance. A business carrying 40 sizes and colours of a product cannot turn stock as fast as one carrying four, and the extra selection may be exactly why customers buy.

The comparison worth making is against your own history and against direct competitors in the same category. A move from 8 to 11 with no increase in stockouts is unambiguously good; a move from 8 to 11 with stockouts rising from 3% to 12% is a business quietly shrinking, and the turnover figure alone reads identically in both cases.