Service Level Calculator
Calculate cycle service level from measured stock-out-free cycles, or from a z value you choose.
In short
Formula: Measured: CSL = cycles without a stock-out ÷ total cycles. Model: CSL = Φ(z), the standard normal probability.
What this calculator does
Calculate cycle service level from measured stock-out-free cycles, or from a z value you choose. Worked example, questions and limitations included.
Use it to turn Method, Replenishment cycles with no stock-out, Total replenishment cycles, Service factor z into a checked result you can compare, copy, or rerun with different assumptions.
The page shows the formula, a numeric worked example, and the assumptions that affect this inventory calculation.
Inputs and what they mean
- Method
- — choice value.
- Replenishment cycles with no stock-out
- — number value.
- Total replenishment cycles
- — number value.
- Service factor z
- — number value.
How to use it
- Enter each value in the unit shown next to the box (use the unit converter first if your numbers are in other units).
- Check the breakdown to see every intermediate step.
- Read the limitations before relying on the result.
Formula
Cycle service level as defined in the ASCM dictionary and Silver, Pyke and Thomas.
Cycle service level (no stock-out in a cycle) is not the same as fill rate (share of demand met).
No target service level is assumed; you supply the counts or z.
Measured: CSL = cycles without a stock-out ÷ total cycles. Model: CSL = Φ(z), the standard normal probability.
Inputs used: Method, Replenishment cycles with no stock-out, Total replenishment cycles, Service factor z.
Worked example
Measured
- 46 ÷ 50 = 92%.
Reading the result
The headline figure is the main answer. Any breakdown underneath shows the parts that make it up, so you can check the working and see what changes when you adjust an input.
Limitations and assumptions
- Model method assumes normality.
- Counts need enough cycles to be meaningful.
- Does not measure shortage size.
- Results are planning estimates built only from the figures you enter. No prices, rates, demand patterns or service levels are built in, and the results are not supplier quotes or carrier rates.
- The result depends on the values you enter for this service level calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.
Common questions
What service level should I target?
That is a business decision balancing stock-out cost and inventory cost. The calculator does not suggest one.
Why is my fill rate higher than this?
A cycle with a small shortage counts as a full failure here, but only a small loss in fill rate. Check the formula, example, and limitations on this page before using the result for a real inventory decision.
What does z = 1.65 represent?
About 95% under a normal model. Choose the model method and enter it to see.
How do I use the Service Level Calculator?
Enter the required values for Method, Replenishment cycles with no stock-out, Total replenishment cycles, Service factor z. The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.
What formula does the Service Level Calculator use?
Measured: CSL = cycles without a stock-out ÷ total cycles. Model: CSL = Φ(z), the standard normal probability. The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone.
Can the Service Level Calculator be used for exact decisions?
Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.
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