Safety stock is the buffer you keep so a busy week or a late supplier does not leave you saying no to a customer. Fill in how much you sell a day, how much that swings, how long your supplier takes and how often you are willing to run out, and you get the buffer to hold.
How many of this one product you ship on a normal working day. Take a recent few months and divide, ignoring holiday shutdowns.
How much a busy day differs from a quiet one. No statistics needed: take your busiest day, subtract your quietest, divide by four. That is close enough.
Days from sending the order to the goods being on the shelf and pickable. Not what the supplier promises: what actually happens, receiving and checking included.
How many days late (or early) your supplier usually is. A supplier who is always three days off is worse for your stock than one who is simply slow but on time.
How often you want to be able to say yes. At 95% you accept running short roughly one time in twenty. Higher is safer and more expensive.
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Safety stock
Units to keep as a buffer, on top of what you sell during the wait for the supplier.
How many normal days of selling that buffer keeps you going.
Units you sell while waiting for the order to arrive.
The multiplier behind your chosen service level. Higher percentage, higher factor, more stock.
A one-page summary with your figures, the method and what the answer means.
The less you have to guess about what is actually on hand, the smaller that buffer can safely be. See what that difference is worth per year.
See what tighter stock levels free upIn plain terms: two things can catch you out. Customers suddenly ordering more than usual, and the supplier turning up later than promised. The bigger those two surprises are, and the less often you are willing to disappoint a customer, the more buffer you need. The calculator uses the standard King formula, which takes both surprises into account instead of just one.
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Those last few percent roughly double your buffer, and you pay for that in cash sitting on a shelf. Choose it per product group: high for your bestsellers and anything a customer would walk away over, low for slow movers with a thin margin.
One promotion, one huge one-off order or one supplier disaster makes the swings look far bigger than they are and inflates the buffer. Take those out of your figures before you trust the result.
For most fast-moving items 95% to 98% is common. Critical or high-margin items justify more; slow movers with low margin rarely do.
Because an unpredictable supplier causes stockouts even when demand is steady. Formulas that only use demand variability systematically understate the stock you need.
Loading metres, floor area, volume and trailers needed, from your own pallet sizes and stacking height.
Volumetric weight calculatorDimensional weight, real weight and the chargeable weight your carrier actually bills.
Warehouse space calculatorSquare metres for a given number of pallet positions, including aisles and support space.
Loading metres, stock levels and order points are only as good as the stock data behind them. That is what a warehouse management system keeps accurate, every movement, without anyone maintaining a spreadsheet.