GMROI Calculator

Written out

Gross margin return on inventory investment is gross margin dollars divided by average inventory at cost. It answers how much gross profit each dollar of stock generates in a year, which is the question turnover and margin each answer only half of.

It can also be written as inventory turnover × (gross margin % ÷ cost of goods %), which makes the trade-off visible: a product can earn its keep through fast turns, fat margins, or a workable combination.

In practice

The example product: gross margin of $40 a unit on 2,080 units is $83,200, against average inventory at cost of $3,132. GMROI is 26.6, every dollar in that stock returns $26.60 of gross margin a year.

That is exceptionally high, because the product combines 69% margin with twelve turns. Most retail is nowhere near it.

A more typical apparel item, three turns and 50% margin, gives 3 × (0.5 ÷ 0.5) = 3.0. A grocery line at twenty turns and 25% margin gives 20 × (0.25 ÷ 0.75) = 6.7. The grocery item looks worse on margin and better on capital, which is exactly the comparison GMROI exists to make.

The limitations

GMROI uses gross margin, so it ignores everything downstream: advertising, fulfilment, returns and the space the product occupies. A high-GMROI product with a 30% return rate may be worse than a lower-GMROI product with none.

It also rewards holding less stock, which can be achieved by understocking. A product with a superb GMROI and frequent stockouts is being flattered by the very failure that is costing sales.

Putting it to use

Use it to compare products competing for the same capital or the same shelf. That is the decision it is built for, and margin or turnover alone will give the wrong answer roughly half the time.

Set a floor rather than a target, a level below which a product has to justify its place in the range. Anything under about 2.0 in general retail is consuming more capital than it returns, and a catalogue usually has a long tail sitting there.

GMROI against GMROS and the space question

Where physical space rather than capital is the binding constraint, the equivalent measure is gross margin return on space, gross margin divided by the square feet or cubic feet occupied. A product with a strong GMROI and a pallet footprint may be the wrong thing to stock in a small warehouse.

For ecommerce with third-party fulfilment, storage is billed by volume, which makes the space version directly calculable and often more decision-relevant than the capital version. A bulky low-value item can show an acceptable GMROI and lose money once storage fees are charged against it.

The practical approach is to calculate whichever version matches the constraint that actually binds. Businesses short of cash should rank on GMROI; businesses short of space should rank on GMROS; businesses short of both should look at each and be suspicious of anything appearing near the bottom of either list.

The ratio is most useful compared within a category rather than across the whole catalogue, since gross margins differ structurally between product types. A GMROI of 2.1 might be excellent in one department and poor in another, and ranking the entire range on a single figure will systematically favour whichever category happens to carry the highest margins.