Enter your stock and sales numbers for any period. The calculator returns the four KPIs that tell you whether your inventory is moving fast enough, or sitting too long.
Example: 500 units on hand at the start of the period.
Example: 200 units received from purchases or transfers during the period.
Example: 320 units shipped or sold through during the period.
Example: 4 weeks (one month). Use fractions for shorter periods.
Example: 380 units physically in stock right now.
Example cost per unit for extended value analysis. Leave blank to skip.
Sell-Through Rate
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Stock-to-Sales Ratio
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Weeks of Cover
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Annualised Inventory Turns
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No single number tells the whole story. Sell-through rate shows what proportion of available stock moved. Stock-to-sales ratio shows how much inventory you hold relative to what you sell. Weeks of cover translates that ratio into time. Annualised turns annualises your sales velocity so you can compare across periods of different lengths.
Used together, they answer the two questions that matter: are you selling what you have, and are you holding too much or too little?
Sell-through rate = units sold ÷ (opening stock + units received). It tells you the percentage of available inventory that actually moved during the period. A rate of 70% means 7 out of every 10 units available were sold.
When to act: Below 50% over a standard retail period usually signals overstock, weak demand, or a pricing problem. Above 90% may mean you are understocked and leaving sales on the table. The target depends on your category — grocery and fast-moving goods run higher; durables run lower.
Stock-to-sales ratio = current on-hand ÷ units sold in the period. It measures how many units of stock you carry for every unit you sell. A ratio of 1.2 means you hold 1.2 units in stock for every unit sold — a tight position. A ratio of 4.0 means you hold four times what you sold — likely excess.
When to act: A rising ratio with flat or falling sales is the earliest warning sign of accumulating dead stock. If the ratio climbs for two consecutive periods without a seasonal explanation, review slow-movers and consider promotions or transfers.
Weeks of cover = current on-hand ÷ (units sold ÷ period weeks). It answers: if sales continue at the current rate, how many weeks until stock runs out? This is the metric most buyers use when placing replenishment orders.
When to act: Below 2 weeks for non-perishable goods usually trigger a reorder, assuming normal lead time. Above 12 weeks for slow-movers often means capital is tied up unnecessarily. Perishable goods need much shorter horizons — check shelf life, not just sales velocity.
Annualised turns = (units sold ÷ period weeks × 52) ÷ average stock. It tells you how many times per year your average inventory position sells out and is replaced. This is the standard metric for comparing performance against industry benchmarks.
When to act: Turns below your category average suggest overstock or slow demand. Turns significantly above average may indicate capital efficiency but also risk of stock-outs. Use turns alongside sell-through rate — high turns with low sell-through can mean you are running very lean, not necessarily performing well.
Inventory Pro tracks sell-through, weeks of cover, and turns automatically for every SKU. Get the numbers every morning without opening a spreadsheet.
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