GPS Speed Calculator

This calculator's straight-line-distance-over-time approach is exactly right for some kinds of travel and a systematic underestimate for others, and understanding which category a given trip falls into is the key to interpreting its result correctly.

For flights and open-water sailing, straight-line (great-circle) distance is often very close to the actual path traveled, since aircraft and ships aren't constrained to follow a road network — a commercial flight's actual route typically hugs close to the great-circle path between departure and arrival airports, adjusted somewhat for air traffic corridors, weather, and fuel-efficient routing, but rarely deviates dramatically from the straight-line distance. For this category of travel, the average speed this calculator produces is a genuinely accurate estimate of real average speed (groundspeed for a flight, or speed-over-ground for a vessel).

For road trips, the calculation tells a different, still-useful story. Roads follow terrain, existing infrastructure, and legal rights-of-way — they curve around obstacles, follow river valleys, and connect through cities rather than cutting directly across the landscape. The actual distance driven on a road trip is almost always meaningfully longer than the straight-line distance between start and end points, sometimes by 10-20% for a fairly direct highway route and substantially more for a winding mountain or coastal road. Because the numerator (distance) in this calculation is smaller than the real distance traveled, the calculated speed will be lower than the actual average driving speed by a proportional amount — a genuinely useful lower-bound sanity check (if this calculation shows an implausibly high number, something is likely wrong with your logged coordinates or timing), but not a precise measurement of real driving performance for road-based travel.

A separate consideration, independent of straight-line versus road distance, is what 'elapsed time' actually includes. If a multi-hour rest stop, a layover, or significant idle time is included in the elapsed hours entered, the resulting average speed reflects total trip time rather than actual moving time — useful for answering 'how fast did I effectively get from A to B including all stops,' but different from 'how fast was I actually moving while in transit.' Both framings are legitimate depending on what you're trying to learn from the calculation; the key is being deliberate about which elapsed-time definition you're using, since the two can produce meaningfully different results for a trip with substantial stopped time.