Table of Control Chart – Constants A2 d2 D3 D4

Control charts are used to calculate control limits and estimate the process standard deviation. Control chart constants used are D4, D3, A2, and d2 (These control chart constants depend on the subgroup size n).

These control chart constants are summarised in the table below. For example, if your subgroup is 4, then D4 = 2.282, A2 = 0.729, and d2 = 2.059.

There is no value for D3. This simply means that the R chart has no lower control limit when the subgroup size is 4.

Sub group Size (n)	A2	D3	D4	d2
2	1.880		3.267	1.128
3	1.023		2.574	1.693
4	0.729		2.282	2.059
5	0.577		2.114	2.326
6	0.483		2.004	2.534
7	0.419	0.076	1.924	2.704
8	0.373	0.136	1.864	2.847
9	0.337	0.184	1.816	2.970
10	0.308	0.223	1.777	3.078
11	0.285	0.256	1.774	3.173
12	0.266	0.284	1.716	3.258
13	0.249	0.308	1.692	3.336
14	0.235	0.329	1.671	3.407
15	0.223	0.348	1.652	3.472
16	0.212	0.364	1.636	3.532
17	0.203	0.379	1.621	3.588
18	0.194	0.392	1.608	3.640
19	0.187	0.404	1.596	3.689
20	0.180	0.414	1.586	3.735
21	0.173	0.425	1.575	3.778
22	0.167	0.434	1.566	3.819
23	0.162	0.443	1.557	3.858
24	0.157	0.452	1.548	3.895
25	0.153	0.459	1.541	3.931