Most of us think that the delivery charge will be given to the delivery guy, but it's not correct. As the product delivery charge is associated with the company it's better to give the tip to the pizza delivery people.
In most of the countries like the United States Pizza delivery is the very hard job with a lot of risk included.
There are some in-depth articles about giving tips to pizza delivery guy at Tip the Pizza Guy
It's better to give 10% tip of the total bill amount to the pizza delivery. To know more about the tip percentages refer this table which shows tip percentages for the corresponding services.
Generally the tip percentage depends on the bill and the distance of delivery. In most cases it's better to give minimum $5 tip.
Giving tip shows our courtesy and satisfaction to their service
To calculate the tip percentage quickly, use this tool TipCalculator.