How to Calculate Distances Between US ZIP Codes: Exploring Free APIs and a Self-Hosted Solution

Calculating distances between postal codes is a key feature for many applications, whether it’s for delivery route optimization, finding nearby stores, or geo-targeted marketing. For developers working with US ZIP codes, there are several free APIs and approaches you can use to achieve this. However, each comes with its own trade-offs.

In this article, we’ll explore popular free APIs to calculate distances between ZIP codes, their limitations, and introduce a self-hosted solution that offers full control and high performance.

Popular Free APIs for ZIP Code Distance Calculation

Zippopotam.us

Zippopotam.us is a simple, free API that provides geographic information, including latitude and longitude, for ZIP codes across many countries including the US.

• Pros: No API key needed, easy to use, free.
• Cons: Only provides location data, so you need to calculate the distance yourself using the coordinates.

To calculate the distance, you’d typically fetch latitude and longitude for each ZIP code, then apply the Haversine formula in your code.

GeoNames

GeoNames offers a web service with a variety of geographic data, including postal codes and their distances.

• Pros: Provides a dedicated postalCodeDistance API endpoint to calculate distances directly.
• Cons: Requires free registration, has usage limits (thousands of requests per day).

It’s a good option if you want a ready-made distance calculation without building your own logic.

OpenStreetMap & Nominatim

OpenStreetMap’s Nominatim service offers geocoding, turning ZIP codes into lat/long coordinates.

• Pros: Free and open source data.
• Cons: No direct distance calculation; you have to implement it. Usage limits apply if you use the public server, so hosting your own instance might be necessary for heavy use.

Google Maps Distance Matrix API

Google’s Distance Matrix API calculates distances and travel times between multiple points.

• Pros: Very accurate routing distances, handles driving, walking, and transit modes.
• Cons: Requires billing account and API key, free tier has monthly usage limits, and depends on an external service.

This is best if you need real-world travel distances instead of straight-line distances.

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The Challenge with Free APIs

While these free options are great to get started or for small projects, they can come with limitations:

• Rate limits and quotas that restrict usage.
• External dependencies can add latency and reliability issues.
• Privacy concerns when sending user location data to third parties.
• Complexity if you have to combine multiple services or implement your own distance calculations.

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Introducing US Zip Distance API: A Fast, Reliable, Self-Hosted Alternative

To overcome these challenges, I developed the US Zip Distance API, a lightweight TypeScript REST API that calculates distances between US ZIP codes using an embedded SQLite database and the Haversine formula.

• Self-hosted: Runs entirely on your own infrastructure, no external dependencies or network calls.
• Fast: Millisecond response times ideal for scalable web and mobile applications.
• Flexible: Supports multiple distance units and returns results sorted by proximity.
• Easy to deploy: Dockerized and simple local setup with full source code included.

This approach gives you full control over your data, usage, and scaling. No surprises or hidden limits.

After purchase, you receive a ZIP archive with the complete project and clear instructions to get started quickly.

If you want to learn more, check it out here:

https://jhonylucas74.itch.io/us-zip-distance-api