How do I make a control chart from measurements?

Paste a header plus time order and measurement columns, or a single column of numbers in the order they were taken. The chart computes the mean and 3-sigma limits from the average moving range. Download the SVG for a report or slide.

What do CL, UCL, and LCL mean?

CL is the average of the points you pasted. UCL and LCL are the upper and lower control limits, conventionally three sigma from that average. A point outside those lines is treated as a special-cause signal. This tool draws the lines. It does not decide what to fix.

Is this an X-bar and R chart?

No. This is an individuals (I) chart of one measurement per time. Subgroup X-bar/R charts need several readings per sample. Paste your subgroup means only if you already computed them; the page will still treat each row as one point.

Does this run Nelson or Western Electric rules?

No. It flags only points beyond ±3 sigma. Runs, trends, and zone rules belong in your notebook. Shewhart is the name of this chart; the page does not replace Minitab’s full rule set.

Is a control chart the same as a Bode plot?

No. A Bode plot is magnitude and phase of a transfer function versus frequency. A Shewhart control chart is a process measurement versus sample number. Use the Bode and Nyquist pages for control theory.

Is the control chart generator free?

The precise, table-driven plot is free to use and free to download as SVG, with no sign-up. Sign in only if you want AI illustrations or other ConceptViz generation tools.

Research Tool

Control Chart Generator for Shewhart SPC

Free control chart generator. Paste sequential measurements to draw a Shewhart I-chart with CL, UCL, and LCL, then download SVG.

Paste sequential measurementsCL, UCL, and LCL from moving rangeOut-of-control points highlightedDownload a watermark-free SVG — free

Paste sequential measurements — renders a Shewhart I-chart with CL, UCL, and LCL as SVG, free

Measurements

Paste a time order plus a measurement, or a single column. This is a Shewhart I-chart. It does not run X-bar/R, Nelson rules, or Bode plots.

25 observations parsed

SigmaTitle

CL / UCL / LCL lines

n=25 · CL=10.007 · σ̂=0.055 · MR̄=0.062 · no points beyond ±3σ. This page does not run Nelson / Western Electric rules.

Control Chart Examples

The first four are exact engine renders from tables. The last two are AI illustrations of Illustration mode.

View:

In control

Exact engine render — pasted measurements, I-chart with 3-sigma limits from moving range.

spcshewhartin-control

Mean shift

Exact engine render — later points sit above UCL.

spcspecial-cause

Wait time

Exact engine render — weekday/weekend wait times in order.

spchealthcare

Bath temperature

Exact engine render — temperature runs in time order.

spclab

AI illustration — Shewhart

AI illustration of Illustration mode — visual mockup, not plotted from measurements.

aiillustration

AI illustration — teaching

AI illustration of Illustration mode — visual mockup, not a fitted process.

aiillustrationteaching

What is a control chart?

A Shewhart control chart plots a process in time order against its own natural variation. The center line (CL) is the mean. The upper and lower control limits (UCL, LCL) are conventionally mean ± 3 sigma. Points inside the limits are consistent with common-cause variation; a point outside is a special-cause signal worth investigating. This page draws an individuals (I) chart from measurements you already have. It does not run X-bar and R charts, CUSUM, EWMA, or Nelson / Western Electric run rules, and it is not a Bode or Nyquist plot from control theory.

How the limits are calculated

Paste a time-order column plus a measurement, or a single column. The default sigma uses the average moving range divided by d2 = 1.128 (n = 2), which is the textbook individuals-chart estimator. Sample standard deviation is an optional second method. Limits are 3-sigma around the mean of the series you pasted.
A run chart is the same series without limits. A histogram ignores time order. A Pareto chart ranks categories, not sequential measurements.

Control chart versus a run chart or Bode plot

Use this page when you want Shewhart limits on a process you already measured. Use a histogram to see the distribution without time. Use the fishbone diagram after a special-cause point to list candidate causes. Do not use this page for Bode / Nyquist / root-locus plots of a transfer function — those live on the control-theory tools.

Export

Download a scalable SVG with no watermark and no account required for the precise plot. The AI Illustration tab is only for slides when you do not have measurements yet — it will not match your process.

Frequently Asked Questions

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What is a control chart?

How the limits are calculated

Paste a time-order column plus a measurement, or a single column. The default sigma uses the average moving range divided by d2 = 1.128 (n = 2), which is the textbook individuals-chart estimator. Sample standard deviation is an optional second method. Limits are 3-sigma around the mean of the series you pasted.

A run chart is the same series without limits. A histogram ignores time order. A Pareto chart ranks categories, not sequential measurements.

Control chart versus a run chart or Bode plot