is there a command or option to show health as a number?

[stabito]

instead of just a green bar with line segments is there an option to just show the number?

[:D]

yes ALT click your health bar it will Inform how much Percent HP and mana you have left.

[Zagryzaec]

He means all the time, so he could manage his damage output better, like culling blade or other.

No there is no such option, but you can
1 know that each notch is 250 if i remember correct
2 possibly change notch amount although i dont remember how and dont know wether its legal.