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For Students
Safety Stock Coverage at different service levels
Safety stock is the margin of error required based on the customer service level and the deviation of the demand during the lead time. The safety stock coverage level is the z-value in standard statistics for calculating the confidence interval for a customer service level.
Safety Stock = Required Inventory Coverage Level * Standard Error of the Demand during the Lead time
Safety Stock = Required Inventory Coverage Level * RMSE * Square-root of (Lead time)
What error measure to use for setting safety stocks? (New article!)
Safety Stock Coverage Values at various required Service Levels ©
| Service Level Required | Inventory Coverage | Incremental Service Level | Incremental Coverage Required | Coverage Level per point increase in Service Level |
50.00% |
0.000 |
|
|
|
70.00% |
0.524 |
0.2000 |
0.524 |
0.02622 |
75.00% |
0.674 |
0.0500 |
0.150 |
0.03002 |
80.00% |
0.842 |
0.0500 |
0.167 |
0.03343 |
80.50% |
0.860 |
0.0050 |
0.018 |
0.03599 |
81.00% |
0.878 |
0.0050 |
0.018 |
0.03656 |
81.50% |
0.896 |
0.0050 |
0.019 |
0.03715 |
82.00% |
0.915 |
0.0050 |
0.019 |
0.03778 |
82.50% |
0.935 |
0.0050 |
0.019 |
0.03845 |
83.00% |
0.954 |
0.0050 |
0.020 |
0.03915 |
83.50% |
0.974 |
0.0050 |
0.020 |
0.03990 |
84.00% |
0.994 |
0.0050 |
0.020 |
0.04069 |
84.50% |
1.015 |
0.0050 |
0.021 |
0.04153 |
85.00% |
1.036 |
0.0050 |
0.021 |
0.04242 |
85.50% |
1.058 |
0.0050 |
0.022 |
0.04338 |
86.00% |
1.080 |
0.0050 |
0.022 |
0.04440 |
86.50% |
1.103 |
0.0050 |
0.023 |
0.04549 |
87.00% |
1.126 |
0.0050 |
0.023 |
0.04666 |
87.50% |
1.150 |
0.0050 |
0.024 |
0.04792 |
88.00% |
1.175 |
0.0050 |
0.025 |
0.04927 |
88.50% |
1.200 |
0.0050 |
0.025 |
0.05074 |
89.00% |
1.227 |
0.0050 |
0.026 |
0.05234 |
| 89.50% |
1.254 |
0.0050 |
0.027 |
0.05407 |
| 90.00% |
1.282 |
0.0050 |
0.028 |
0.05597 |
90.50% |
1.311 |
0.0050 |
0.029 |
0.05806 |
91.00% |
1.341 |
0.0050 |
0.030 |
0.06035 |
91.50% |
1.372 |
0.0050 |
0.031 |
0.06290 |
| 92.00% |
1.405 |
0.0050 |
0.033 |
0.06574 |
| 92.50% |
1.440 |
0.0050 |
0.034 |
0.06892 |
| 93.00% |
1.476 |
0.0050 |
0.036 |
0.07252 |
93.50% |
1.514 |
0.0050 |
0.038 |
0.07662 |
94.00% |
1.555 |
0.0050 |
0.041 |
0.08134 |
94.50% |
1.598 |
0.0050 |
0.043 |
0.08684 |
| 95.00% |
1.645 |
0.0050 |
0.047 |
0.09332 |
| 95.50% |
1.695 |
0.0050 |
0.051 |
0.10109 |
| 96.00% |
1.751 |
0.0050 |
0.055 |
0.11058 |
| 96.50% |
1.812 |
0.0050 |
0.061 |
0.12245 |
| 97.00% |
1.881 |
0.0050 |
0.069 |
0.13777 |
97.50% |
1.960 |
0.0050 |
0.079 |
0.15834 |
| 98.00% |
2.054 |
0.0050 |
0.094 |
0.18757 |
98.10% |
2.075 |
0.0010 |
0.021 |
0.21106 |
| 98.20% |
2.097 |
0.0010 |
0.022 |
0.22073 |
| 98.30% |
2.120 |
0.0010 |
0.023 |
0.23144 |
98.40% |
2.144 |
0.0010 |
0.024 |
0.24339 |
| 98.50% |
2.170 |
0.0010 |
0.026 |
0.25680 |
| 98.60% |
2.197 |
0.0010 |
0.027 |
0.27196 |
98.70% |
2.226 |
0.0010 |
0.029 |
0.28925 |
| 98.80% |
2.257 |
0.0010 |
0.031 |
0.30917 |
98.90% |
2.290 |
0.0010 |
0.033 |
0.33239 |
99.00% |
2.326 |
0.0010 |
0.036 |
0.35980 |
| 99.10% |
2.366 |
0.0010 |
0.039 |
0.39270 |
99.20% |
2.409 |
0.0010 |
0.043 |
0.43297 |
99.30% |
2.457 |
0.0010 |
0.048 |
0.48348 |
| 99.40% |
2.512 |
0.0010 |
0.055 |
0.54881 |
| 99.50% |
2.576 |
0.0010 |
0.064 |
0.63685 |
| 99.60% |
2.652 |
0.0010 |
0.076 |
0.76241 |
99.70% |
2.748 |
0.0010 |
0.096 |
0.95712 |
| 99.80% |
2.878 |
0.0010 |
0.130 |
1.30380 |
99.90% |
3.090 |
0.0010 |
0.212 |
2.12071 |
| 99.95% |
3.291 |
0.0005 |
0.200 |
4.00589 |
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