Distance between cities: what you’re actually calculating

When people ask “How far is City A from City B?”, they usually mean one of two things: (1) the driving distance along roads, or (2) the straight-line distance between two points on Earth. This calculator focuses on the straight-line version, which is also called the great-circle distance.

A “great circle” is the largest possible circle you can draw on a sphere. The equator is a great circle. If you stretched a tight string around a globe between two points, it would align along a great-circle path. That path is the shortest distance over the Earth’s surface (ignoring elevation).

Why is this useful? Because it’s fast, consistent, and great for planning. If you’re comparing travel options, estimating flight time, or simply curious whether two cities are closer than you thought, great-circle distance is the cleanest baseline. It also powers many real-world systems (navigation math, aviation planning, and geospatial tools).

• City fields: If you choose a city from the list, we use its saved coordinates.
• Coordinates (Advanced): Latitude/longitude let you calculate from any exact point.
• Units: Kilometers (km) or miles (mi). Internally we calculate in km and convert if needed.
• Speed estimates: Optional average speeds to estimate travel time (not route-aware).

It’s simple and shareable. A straight-line distance is a single number that doesn’t depend on which road you take or which airline route exists today. That makes it perfect for: trip brainstorming, fun comparisons (“Wait… LA is THAT far from NYC?”), and quick sanity checks when you’re planning a weekend or calculating whether a commute is realistic.

The Haversine formula (great-circle distance)

Earth is roughly spherical, so the “flat map” distance formula doesn’t work well for cities far apart. Instead, we convert each location into latitude/longitude angles and compute the arc distance along the sphere. The most common approach is the Haversine formula.

• Convert latitude/longitude from degrees to radians.
• Compute the differences Δlat and Δlon.
• Use Haversine to find the central angle between the two points.
• Multiply that angle by Earth’s radius (≈ 6371 km) to get distance.

The Haversine formula computes an intermediate value “a” that represents the squared half-chord length between points, then uses an inverse trig step to get the central angle “c”. Finally, distance = R × c. In this calculator we use R = 6371 km (a standard average Earth radius) and then convert to miles if requested.

• Short hop: City pairs within ~50–200 km often feel like “same region.”
• Weekend trip: 200–800 km is a classic road trip range.
• Long haul: 3000+ km usually means flights, time zones, or overnight travel.

Note: Earth isn’t a perfect sphere (it’s slightly squashed). For most city-to-city use cases, Haversine is accurate enough. Extremely precise surveying would use an ellipsoidal model, but that’s overkill for everyday planning.

How the time estimates are calculated

After we compute the straight-line distance, we provide simple time estimates for driving, train, and flying. These are not route-based. They are computed using: time = distance ÷ speed.

• Driving: 60 mph (or 100 km/h)
• Train: 90 mph (or 145 km/h)
• Flight: 500 mph (or 800 km/h)

These defaults are intentionally “reasonable averages.” Real-world travel time can change dramatically: traffic, stops, terrain, connections, airport check-in, and detours are not included. But as a quick comparison tool, these estimates help answer questions like: “Is this drivable in a day?” or “Is flying obviously better?”

• If you know you’ll be driving slow roads (set 40–50 mph).
• If you’re estimating high-speed rail segments (set 150–200 mph).
• If you’re planning a short flight where overhead dominates (time estimate will be optimistic).

Frequently Asked Questions

• Is this driving distance or straight-line distance?

  This is straight-line (great-circle) distance. Driving distance is usually longer because roads aren’t perfectly straight.

• Why do I see different numbers on Google Maps?

  Google Maps shows route-based distance (roads). This calculator uses the shortest surface path on a sphere (Haversine). Both are “correct” for different definitions of distance.

• What if my city isn’t in the list?

  Type any label and open Advanced, then enter the latitude/longitude for both points. You can find coordinates from many sources (including map apps), then paste them here.

• How accurate is Haversine?

  For city-to-city planning it’s typically very accurate. For ultra-precise geodesy you’d use an ellipsoid model, but that’s beyond what most people need.

• Can you calculate “flight distance” exactly?

  Real flight paths depend on air corridors, wind, and airline routing. Great-circle is the standard baseline estimate.