import tkinter as tk
import tkinter.font as tkfont

root = tk.Tk()

font_tuple = ("Calibri", -14)
font = tkfont.Font(root, font_tuple)

lb1 = tk.Label(root, text="Hello", font=font_tuple)
lb1.pack()
lb2 = tk.Label(root, text="Hello", font=font)
lb2.pack()

root.update()
print(lb1.winfo_width(), lb1.winfo_height())
print(lb2.winfo_width(), lb2.winfo_height())

root.mainloop()