diff --git a/src/distance.rs b/src/distance.rs
new file mode 100644
index 0000000..17eeefe
--- /dev/null
+++ b/src/distance.rs
@@ -0,0 +1,17 @@
+const EARTH_RAD_METERS: f64 = 6371e3;
+
+type LatLon = (f64, f64);
+
+pub fn haversine(a: LatLon, b: LatLon) -> f64 {
+    let a_latitude = a.0.to_radians();
+    let b_latitude = b.0.to_radians();
+
+    let delta_latitude = (b.0 - a.0).to_radians();
+    let delta_longitude = (b.1 - a.1).to_radians();
+
+    let central_angle_inner = (delta_latitude / 2.0).sin().powi(2)
+        + a_latitude.cos() * b_latitude.cos() * (delta_longitude / 2.0).sin().powi(2);
+    let central_angle = 2.0 * central_angle_inner.sqrt().asin();
+
+    EARTH_RAD_METERS * central_angle
+}