How to fix button width in tkinter if I want to put text in it?

Question

I tried to put some text in a button. But the pre-set size changed, to the text's size

so this is the code:

frame = tk.Frame(master=gridframe, width=15, height=15, borderwidth=0, bg=mzcolor)
frame.grid(row=1, column=1)
button = tk.Button(master=frame, text=f"●", font=("System", 10), width=15, height= 15, fg="black", bg="red", relief=tk.RIDGE)
button.pack()

So how can I keep the pre-set sizes? Any Ideas?