Is there some way (command, request,...) in Groff to measure the height of a string or character?

I'm working on a preprocessor to draw the square root for the equation (attempt to improve aesthetic of the EQN equation) which involves finding the size (width and height) of the string. I've found request/command and register that return the width of the string or character like \w'H', but I can't find the request/command to return the height. Is there some to way to find the height? Thank you so much.