Speed Calculator
Solve any corner of the speed–distance–time triangle. Pick what to find, enter the other two, and get the answer in mph, km/h, m/s, and knots at once — plus the equivalent running pace per mile and per kilometer.
Average speed over the whole trip — stops count against you. 1 knot = 1 nautical mile per hour = 1.151 mph.
Speed = distance ÷ time (and the other two ways around)
One relationship, three rearrangements: speed = distance ÷ time, distance = speed × time, time = distance ÷ speed. Everything here is average speed — a 300-mile drive completed in 5 hours averaged 60 mph regardless of what the needle touched. The calculator normalizes to meters and seconds internally, so you can mix units freely: miles with a hh:mm:ss time, or knots with nautical miles.
Runners flip speed into pace (time per distance): 6.55 mph is a 9:10/mile pace, since pace = 60 ÷ speed in minutes per mile. Sailors and pilots use knots — nautical miles per hour — because a nautical mile is one minute of latitude, which makes chart math clean.
How it’s calculated
All inputs convert to SI (mile = 1,609.344 m; nautical mile = 1,852 m; knot = 0.5144 m/s; mph = 0.44704 m/s), the missing variable is solved, and results convert back out. Pace (min/mi) = 26.8224 ÷ (m/s); pace (min/km) = 16.6667 ÷ (m/s).
Constant-average calculation — for point-to-point travel planning, add stop and traffic time on top.
Worked example
A marathon — 26.2 miles in 4:00:00 — is an average of 6.55 mph (10.54 km/h, 2.93 m/s, 5.69 knots), a pace of 9:10 per mile (5:42 per km). Solving the other way: 300 miles at 65 mph takes 4 h 37 m, and a 10 km race finished in 55:00 means you averaged 10.91 km/h (6.78 mph).
Common mistakes
- Entering 4:30 (four and a half hours) as 4.3 hours — use the separate minutes field.
- Confusing pace with speed: a lower pace number is faster, a lower speed is slower.
- Averaging speeds of two trip legs arithmetically — equal distances at 30 and 60 mph average 40 mph, not 45.
- Forgetting stops: rest breaks and traffic drop your door-to-door average well below cruising speed.
Where it is used
- Estimating arrival times for drives, rides, flights, and passages.
- Converting race results between pace, speed, and finish time.
- Marine and aviation planning in knots and nautical miles.
- Physics homework: solving v = d/t in any unit system.
Frequently asked questions
How do I convert speed to running pace?
Pace (min per mile) = 60 ÷ speed in mph: 6 mph is a 10:00 mile, 7.5 mph an 8:00 mile. For kilometers, pace = 60 ÷ km/h — 12 km/h is 5:00/km. The pace line does both automatically.
What exactly is a knot?
One nautical mile (1,852 m) per hour — 1.151 mph or 1.852 km/h. A nautical mile equals one minute of latitude, which is why ships and aircraft navigate with it. 20 knots ≈ 23 mph.
Why is my average speed lower than my cruising speed?
Averages include every slow mile and stop. Cruise at 70 mph but take a 30-minute break in a 4-hour trip and your average drops to about 61 mph. For ETAs, divide total distance by realistic door-to-door time.
How do I average the speed of two legs?
Total distance ÷ total time — never the midpoint of the two speeds. Drive 60 miles at 30 mph then 60 miles at 60 mph: 120 miles in 3 hours = 40 mph average.
What is a quick m/s conversion trick?
Multiply m/s by 3.6 for km/h and by roughly 2.24 for mph. Usain Bolt’s 12.4 m/s peak is 44.7 km/h or about 27.8 mph.