Speed Converter — Free
Runs 100% in your browser — your files never leave your device.
Roads post kilometers per hour, aviation and sailing speak knots, physics uses meters per second, and old signage still says miles per hour. Enter any speed and every other unit updates at once, from exact definitions of the mile, foot, and nautical mile.
How it works
- 1
Type a speed
Any of the five units can be the one you start with.
- 2
Watch the rest fill in
Road, air, and scientific speeds all describe the same motion.
- 3
Compare with reference points
Walking, highway, and sound-barrier speeds sit in the guide below.
About this tool
Why knots exist
One knot is one nautical mile per hour — exactly 1.852 km/h. The nautical mile was tied to one arc-minute of latitude, so a navigator could read distance straight off a chart without arithmetic. That convenience outlived the sailing ships: aviation and maritime speed still answer in knots.
Quick comparisons
A brisk walk is about 5 km/h (3 mph); motorways run 100–130 km/h (62–81 mph, 54–70 knots); sound at sea level is about 343 meters per second — 1,235 km/h or 767 mph. Converting the time units underneath these? The time converter turns hours into seconds.
Frequently asked questions
Is one knot the same as one mile per hour?
No — a knot is 1.15078 mph, because the nautical mile is longer than the land mile. At sea, that gap matters for fuel and eta plans.
How do I convert km/h to mph quickly?
Divide by 3.6. For a rough mental figure, take off a little more than a fifth: 100 km/h is just over 60 mph.
Why do aircraft use knots instead of mph?
Because charts measure distance in nautical miles — one per minute of latitude — so knots keep speed, distance, and navigation on the same ruler.