From smallest to largest, with most commonly chambered calibers listed...
M -- 7-shot .22 LR only. Made prior to and just after WW I. 3 separate models, EXTREMELY desirable for collectors.
I -- .22, .32 Long, and .38 S&W. The I-frame .32 Hand Ejector was the FIRST S&W Hand Ejector, introduced in 1896, 3 years before what became known as the K-frame. A very few reportedly were factory made in .32 S&W; an authentic one would be worth a lot of money.
I Improved -- Same size as the I-frame, with the same calibers. It introduced the coil mainspring.
J -- .22, .22 Mag., .32 Long, .32 Mag., .38 Spl., .357 Mag., 9mm. Introduced post WW II, and made concurrently with the I frame for a number of years. Introduced because the I frame was too short for the .38 Spl.
K -- .22, .32 Long, .32-20, .38, .357, and others.
L -- .357 Mag. (predominantly), .44 Spl. recently, .38 Spl. as special order, and possibly a few others. Introduced in the early 1980s as a beefed up K frame to give better life with .357 Mag. ammo.
N -- .38 Spl., .357 Mag., .41 Mag., 10 mm, .44 Spl., .44 Mag., .45 ACP, .45 Colt, and many many others. Largest of all of S&W's frame sizes for the big cartridges.
One thing of interest.
While most people refer to the stainless steel guns as being J, K, L, N frames, etc., they really aren't. The factory has a different set of letters that are used for referring to the frames on those firearms.