Speed Distance Time Calculator
Calculate speed, distance, or time with multi-unit support and real-world context.
Enter Known Values
Results
km/h
50
mph
31.069
m/s
13.889
knots
26.998
Real-World Context
At this speed, New York to LA (2790 mi) would take 89.79 hours.
Speed (m/s)
13.889
Distance (m)
100,000
Time (s)
7,200
Distance vs Time (at constant speed)
Speed Distance Time Calculator
Calculate speed, distance, or time with multi-unit support including km/h, mph, m/s, knots, and more.
Guide
How it works
Speed vs. Velocity: An Important Distinction
Speed is a scalar quantity — it has magnitude only. Velocity is a vector — it has both magnitude and direction. A car traveling at 60 mph north has speed 60 mph and velocity 60 mph N. If it turns around at 60 mph, its speed remains 60 mph but velocity reverses. This distinction matters enormously in physics: a ball thrown upward decelerates (velocity decreases) even though its speed magnitude changes continuously.
Terminal Velocity
When a skydiver jumps from a plane, gravity accelerates them downward, but air resistance increases with speed. Eventually the drag force equals gravity, and acceleration stops — this is terminal velocity. In a spread-eagle position, a skydiver reaches about 195 km/h (120 mph). In a head-down dive position, terminal velocity can exceed 290 km/h (180 mph). The world record for free-fall speed (in a spacesuit from 39 km altitude) was 1,357 km/h — exceeding the speed of sound.
Speed of Sound and Mach Number
Sound travels at approximately 343 m/s (1,235 km/h) in dry air at 20°C. Speed varies with temperature: roughly 0.6 m/s per °C. The Mach number is the ratio of an object's speed to the local speed of sound. Mach 1 (breaking the sound barrier) creates a sonic boom. The Concorde cruised at Mach 2.04 (2,179 km/h). Light travels at 299,792,458 m/s — about 874,030 times the speed of sound.
GPS Speed Measurement
GPS devices measure speed by calculating position change over time — essentially distance ÷ time over very short intervals. Modern GPS chips sample position every 0.1–1 seconds with accuracy of ~2–5 meters, giving speed accuracy of about ±0.1 km/h. Dedicated sports GPS units sample at 10 Hz (every 0.1 seconds) for more accurate speed during rapid acceleration, like in sprint analysis.
Reaction Distance and Braking
At 60 mph (~27 m/s), during the average human reaction time of 1.5 seconds, a car travels ~40 meters (131 feet) before the driver even touches the brakes. Total stopping distance (reaction + braking) at 60 mph on dry pavement is approximately 73 meters (240 feet). At 120 mph, reaction distance doubles to 81 meters and total stopping distance quadruples — because braking distance scales with the square of speed. This physics is why speed limits are set low.
The 85th Percentile Rule in Traffic Engineering
Traffic engineers set speed limits using the 85th percentile rule: the speed at or below which 85% of vehicles travel naturally (without enforcement) on a given road. This is considered the safest and most effective limit, balancing compliance with safety. Roads where the posted limit is far below the natural 85th percentile see more accidents due to speed variance between drivers — the speed difference between vehicles is a stronger predictor of accidents than absolute speed.
How do I calculate average speed for a round trip?expand_more
You cannot simply average the two speeds. Average speed = total distance / total time. For example, 60 mph there and 40 mph back over equal distances: total distance = 2d, total time = d/60 + d/40 = 5d/120. Average speed = 2d / (5d/120) = 48 mph — the harmonic mean, not the arithmetic mean.
What is the difference between knots and mph?expand_more
A knot is 1 nautical mile per hour. One nautical mile = 1,852 meters, compared to a standard mile = 1,609 meters. So 1 knot ≈ 1.151 mph or 1.852 km/h. Knots are used in aviation and maritime navigation because nautical miles directly correspond to degrees of latitude on Earth's surface.
How long does it take light to travel from the Sun to Earth?expand_more
The average Earth-Sun distance is ~149.6 million km. Light travels at 299,792 km/s. Time = 149,600,000 / 299,792 ≈ 499 seconds, or about 8 minutes 19 seconds. This is why we see the Sun as it was 8 minutes ago — a concept called light travel time.
What is relative speed?expand_more
Relative speed is how fast two objects move with respect to each other. Two cars moving in the same direction at 60 mph and 80 mph have a relative speed of 20 mph. Moving toward each other, their relative speed is 140 mph. This is used in collision physics, satellite orbital mechanics, and everyday driving safety calculations.
How do I convert m/s to km/h?expand_more
Multiply by 3.6. This is because 1 m/s × 3,600 seconds/hour ÷ 1,000 meters/km = 3.6 km/h. To go from km/h to m/s, divide by 3.6. For example, 100 km/h = 100/3.6 ≈ 27.8 m/s.