Choose a column that contains the same spacing for each line from top to bottom
Measure baseline (bottom of font) from the top line to baseline to last line in millimeters

Divide mm height by number of lines
158mm / 59 lines = 2.678mm

Convert mm to inches
2.678mm / 25.4mm = 0.1054 inches

Convert inches to points
0.1054 inches x 72 = 7.5888 point font

[Reference: 72 points per inch and 25.4 mm per inch]

Schuyler RSV Quentel with Apocrypha

182 / 45 lines = 4.04mm
4.04mm / 25.4 = 0.15923
0.15923 x 72 = 11.8 point font
(Includes the leading or space between the characters)
Published font by Schuyler: 10pt Milo

The smallest font that I am able to comfortably read for extended periods of time is 8.2pt on 8.5pt Lexicon as published by Cambridge in the ESV Diadem edition. However I prefer the example from above as published by Schuyler in the RSV edition.

Here are some examples of Bibles I currently own

Cambridge NRSV w/apoc = 9.3pt
Cambridge ESV Diadem = 8.4pt
Cambridge Topaz = 10.5pt
Schuyler ESV Stridon = 11.1pt
Schuyler RSV Quentel w/ apoc = 11.4pt
Crossway ESV Study Bible = 9.9pt