This simple online calculator gives a vertical object shadow length for specified day and geographic coordinate. The calculator uses Sun position algorithm to calculate sun altitude.
Then it uses this formula to calculate shadow length:
h - object height,
a - angle between Sun and horizon.
The calcultor gives zero result if there is no shadow. As you know, this may happen at night time :).
Save the calculation to reuse next time, to extension embed in your website or share share with friends.
You may also calculate the shadow growth during the whole day using the calculator below: