The emphasis on theoretical is due to the fact that most rolling mills (manufacturers of sheet metal) will maximize the square footage and minimize the thickness.

Note that nonferrous gages (aluminum) are not the same as ferrous gages (steel & stainless)!

Material thickness:

	ALUMINUM		STEEL
(mm)	(inches)	Gage	(inches)	(mm)
5.827	.2294	3	.2391	6.073
5.189	.2043	4	.2242	5.695
4.620	.1819	5	.2092	5.314
4.115	.1620	6	.1943	4.935
3.665	.1443	7	.1793	4.554
3.264	.1285	8	.1644	4.176
2.906	.1144	9	.1495	3.797
2.588	.1019	10	.1345	3.416
2.304	.0907	11	.1196	3.030
2.052	.0808	12	.1046	2.657
1.829	.0720	13	.0897	2.278
1.628	.0641	14	.0747	1.897
1.450	.0571	15	.0673	1.709
1.290	.0508	16	.0598	1.519
1.151	.0453	17	.0538	1.367
1.024	.0403	18	.0478	1.214
0.912	.0359	19	.0418	1.062
0.813	.0320	20	.0359	0.912
0.724	.0285	21	.0329	0.836
0.643	.0253	22	.0299	0.759
0.574	.0226	23	.0269	0.683
0.511	.0201	24	.0239	0.607
0.455	.0179	25	.0209	0.531
0.404	.0159	26	.0179	0.455
0.361	.0142	27	.0164	0.417
0.320	.0126	28	.0149	0.378
0.287	.0113	29	.0135	0.343
0.254	.0100	30	.0120	0.305
0.226	.0089	31	.0105	0.267
0.203	.0080	32	.0097	0.246
0.180	.0071	33	.0090	0.229
0.160	.0063	34	.0082	0.208
0.142	.0056	35	.0075	0.191