SPC Calculations

Prior to conducting SPC calculations for the X bar and R chart make sure you gather your data. When gathering the data keep in mind these guidelines.

  • Select a sample size from 2 – 8 parts*.
  • Collect at least 25 groups of samples
  • Take the data over a period of a couple days
  • Select random lots and parts
  • Select random operators and machines.
  • Plot the data on a histogram and assure the data is normally distributed.

* Do not change the sample size after you start collecting your data and plotting the points.

Learn SPC in an hour. Train your employees. Improve your processes and products. Prevent defects and save your company money.

SPC Training Video

Limit Calculations

1) For each group of samples calculate the mean and the range.

2) Calculate the overall mean which is know as  

3) Calculate the mean of all of the ranges. This is known as

4) Now you are ready to calculate the limits. See below for the equations

Learn SPC in an hour. Train your employees. Improve your processes and products. Prevent defects and save your company money.

SPC Training Video

Here is the table for the constants. The constants depend on your sample size.

Comment Box is loading comments...

More Info

  • SPC Help Video

    Download Today. The number one mistake company’s make when implementing SPC is not training their employees in SPC. Maximize your SPC efforts! Get SPC help. Use this SPC Training Video to quickly train your staff. $59.00. Satisfaction guaranteed.

  • Control Chart SPC, Control Charts and limits

    Learn about control chart SPC and the differences between process limits and specification. Includes pictures of these limits with control charts.

  • Auditing SPC inspection

    Learn to audit your SPC inspection program. This article covers SPC technology keys such as documentation, training, reviewing, and process improvement.

  • SPC definition

    Here we discuss the SPC definition. We describe the charts and the meaning of "special cause variation". Read more...

  • statistical process control

    This article covers a roadmap for statistical process control. Discusses chart structure and implementation mistakes.

  • Control Charts

    Control Charts, Variable data, Attribute data, Variation, Total Quality Management Tool

  1. QAS Home
  2. >
  3. SPC
  4. >
  5. SPC Calculations

Quality Assurance Solutions
Robert Broughton
(805) 419-3344
Unique QA Products

All Products

Software, Videos, Manuals, On-Line Certifications

8D Manager

Corrective Action Software

Snap Sampling Plans!

AQL Inspection Software

TrainingKeeper Software

Plan and Track Training

StreamLiner Software

Lean and Continuous Improvement

Statistical Process Control

Training Video

ISO 9001:2015 QA Manual

Editable Template

ISO Calibration Manual

Editable Template

ISO 9001:2015 QMS Kit

Templates, Guides, QA Manual, Audit Checklists

ISO 14001:2015 EMS Kit

EMS Manual, Procedures, Forms, Examples, Audits, Videos

On-Line Accredited Certifications

Six Sigma, Risk Management, SCRUM

All Products

Software, Videos, Manuals, Training Material

Please Recommend Us!