Difference between k or M

Hello il New at rise of Berk. Which dragon is stronger ? The one with 945 k or the one with 2.75 m/h

Your units don’t make sense; did you mean k/h vs. M/h (e.g. 850k/h vs. 2.5M/h)?

Assuming that’s what you meant, you might want to brush up on standard metric prefixes.

k = 1e3 ⇒ 850k = 850,000
M = 1e6 ⇒ 2.5M = 2,500,000

(Strictly speaking, there is some rounding; 2.5M might actually be something like 2,498,320.)

Eventually, you’ll encounter G as well, at least for storage capacity and duties.