from tkinter import *
root = Tk()
root.title("Pés para metros")
root.geometry("300x150")
root.resizable(False,False)
def calcular(*args):
    try:
        value = float(pes.get())
        a = (0.3048 * value * 10000.0 + 0.5) / 10000.0
        araoun = round(a,3)
        metros.set(araoun)
    except ValueError:
        pass
pes = DoubleVar()
metros = StringVar()
pes_entry = Entry(textvariable=pes,justify='center')
pes_entry.place(relx=0.15,rely=0.05,relwidth=0.2)
pes_texto = Label(text="Pés",font=("arial","13"))
pes_texto.place(relx=0.45,rely=0.05)

texto1 = Label(text="é equivalênte a ",font=("arial","13"))
texto1.place(relx=0.05,rely=0.4)
resultadosmetros = Label(textvariable=metros,font=("arial","13"),
                         bg="black",justify='center',fg="white")
resultadosmetros.place(relx=0.45,rely=0.4,relwidth=0.25)
texto2 = Label(text="metros.",font=("arial","13"))
texto2.place(relx=0.7,rely=0.4)
butao= Button(text="Calcular",font=("arial","12",'bold'),
              bg="blue", command=calcular)
butao.place(relx=0.35,rely=0.7,relwidth=0.3,relheight=0.2)
root.mainloop()