Radius and Distance Formula

ZIP Code Download's Distance and Radius Assistants

One of the most common questions we are asked at ZIP Code Download is related to adding a vendor or store finder to a website. These finder services are invaluable when trying to connect potential customers with the services you are promoting. To assist developers with providing this information to their customers, ZIP Code Download offers a radius and distance API with the distance formula and radius formula.

Our radius and distance formula APIs calculates the distance between ZIP codes using the sphere-earth model. This formula is far superior to the flat-earth model that is used in many ZIP code formulas. The radius and distance APIs include all the formulas necessary to build an effective finder tool for most organizations.

Understanding the difference between the distance and radius APIs is very important when making a purchase. Both tools can be used separately to achieve decent results, but it is when they are used together that the distance and radius formulas are most effective. The distance tool will calculate the distance between all the ZIP codes in the country and return any ZIP codes that match the distance criteria that the user specifies. Even though there are more than 40,000 ZIP codes, this can be done fairly quickly.

The radius tool, on the other hand, would be less effective on its own. The radius tool works by drawing a box around the ZIP code (based on the latitude and longitude coordinates). The distance tool will then only calculate the distances between the requested ZIP code and the ZIP codes within the box created by the tool. Without the distance tool, you would approximately get the ZIP codes within the radius, but there some ZIP codes may be returned that are slightly outside the radius requested.

Along with the distance and radius formula API, you will need to purchase a ZIP code database with latitude and longitude coordinates for the tools to work correctly. All of these products are available from ZIP Code Download.

Distance Formula
Radius Formula
ZIP Code Latitude and Longitude Database