How To Calculate Upper And Lower Warning Limits

Calculating upper and lower warning limits is crucial in statistical process control to monitor and maintain product quality. It helps identify out-of-control processes and ensures consistent output.

1. Enter the mean and standard deviation of your process.
2. Select your desired confidence level.
3. Click ‘Calculate’.

The calculator uses the following formula to calculate warning limits:

Upper Warning Limit = Mean + Z * Standard Deviation

Lower Warning Limit = Mean – Z * Standard Deviation

Where Z is the value from the standard normal distribution corresponding to the chosen confidence level.

Comparison of Warning Limits at Different Confidence Levels

Confidence Level	Z Value	Upper Warning Limit	Lower Warning Limit
95%	1.96	12.7	7.3
99%	2.58	15.5	4.5

• Regularly review and update warning limits as process parameters change.
• Use control charts to monitor process performance and identify trends.

What are control limits?

Control limits are the upper and lower bounds within which a process is considered to be in statistical control.

For more information, see the Upper and Lower Control Limit Calculator from iSixSigma.