There is a Color Contrast Calculator conveniently built into the Accessibility Inspector. Find it in Window, in the top menu. Select two colors for text and background and check if it passes for all text sizes or just some of the largest ones.

With the Accessibility Inspector open, select Window in the top menu, and then Show Color Contrast Calculator. It will open on a separate window. Two colors can be selected for text and background in a few ways, like specifying RGB or Hex values. You can then move the text size slider to find out if it passes for all the text sizes or just some of the largest sizes.