How is safety stock calculated?

There are several different methods to calculate safety stock. The method you choose depends on the purpose the safety stock will serve. If you are trying to cover inconsistencies within your supply chain then you may just use the variance times your demand rate: so if you have a 5 day delivery variance and a demand rate of 100 units a day, your safety stock would be 5 * 100 or 500.

If you are trying to cover demand fluctuations the process will be a little more in-depth and will depend on the level coverage you wish to obtain. Lets say that over the course of a year, you find that a particular part has a demand standard deviation of 10 and you wish to have inventory 99.7 percent of the time then you will multiply 3 * 10 equal 30.

Safety stock is typically done as a last resort and never should be used as a permanent corrective action. Anytime you have inventory over and above the demand, you are adding cost along your supply chain.