lwjgl, SLick-util - fixating string midpoint to a coordinate.

Engines, Libraries and Tools
#1

I have ammo counter and it varies in length depending on how much ammo is left. Im using

RenderThread.graphics2D.drawString(20, 55, weapon.getAmmo() + "/" + weapon.getMaxAmmo());

to draw the ammo counter. Problem is the x and y coordinates are the upper left coordinates. but i would like to get the midpoint coordinates. So that no matter how much ammo is used the “/” is still at the same exact coordinates. How can it be done?