(a) candella = 1000mcd
(b) lumen divided by 12.57 = 1 candella
answer from (b) x 1000 gives mcd
this will give you a rough comparison.
Also, alot depends on the lens used, a brighter source that is wider difused will "look" dimmer than a closely focused source that is weaker.
Strictly speaking, there is no direct conversion. The units are measured in diferent ways, and involve a bit of "fudging" of numbers due to historical reasons and SI unit conventions, colour, etc. Long boring story. We use a light meter calibrated to human eye sensitivity when comparing light sources at work ( we use LED, incandescent, and halogen lamps at work on emergency vehicles and their output must match a government specification for light output. )