Python 101: Hot-tub water volume

# Futurelearn: Python 101 from RPi Foundation - Hot Tub Volume
from math import pi

print("Hi, I am your personal 'bot' called Sam.  \nI will work out how much water you need in a circular hot-tub!\n")

users_name = input("Please enter your name: ")
print("Welcome " + users_name + "!")

print("\nFirst, let's get some numbers...")
diameter = input("How wide, in metres, is the inside of your circular hot-tub? ")
height = input("How high up, in metres, should the water be in your hot-tub? ")

radius = round(float(diameter)/2,2)
height_cast = float(height)

volume = round(pi * radius * radius * height_cast,2)
output = str(volume)
print("\nFor a hot-tub with a diameter " + diameter + " metres and water height " + height + " metres, the volume of water is " + output + " cubic metres.")