Use the result as a scenario, not a black box
Gross margin tells you how much revenue remains after inventory cost. Operating margin goes further by subtracting labor, rent, software, security and other operating expenses you enter. The result is useful for scenario planning because you can immediately see whether a pricing change, purchasing improvement or overhead reduction has the biggest effect.
How the math works
Gross profit = revenue − COGS. Gross margin = gross profit ÷ revenue. Operating profit = gross profit − labor − overhead − other fees. Operating margin = operating profit ÷ revenue.
A store with $250,000 in net sales and $135,000 of COGS has $115,000 of gross profit, a 46% gross margin. After $42,000 labor, $36,000 overhead and $12,000 other expenses, the simple operating profit is $25,000, or 10%.