Speed Calculator

Formula

Speed = Distance ÷ Time

Speed equals distance divided by time. Rearrange to find distance (S×T) or time (D÷S). Ensure consistent units.

Worked Examples

Example 1: Road Trip Planning

Problem:How long will it take to drive 450 km at an average speed of 90 km/h?

Solution:Time = Distance ÷ Speed Time = 450 km ÷ 90 km/h Time = 5 hours Add 15-20% for stops and traffic: Total trip time ≈ 5.75-6 hours

Result:5 hours driving (6 hours total)

Example 2: Running Pace

Problem:A runner completes a 10K race in 50 minutes. What was their speed?

Solution:Distance = 10 km Time = 50 min = 0.833 hours Speed = 10 ÷ 0.833 = 12 km/h Pace = 50 ÷ 10 = 5 min/km In mph: 12 ÷ 1.609 = 7.46 mph

Result:12 km/h (7.46 mph, 5:00/km pace)

Example 3: Flight Distance

Problem:An airplane flies at 850 km/h for 3.5 hours. How far did it travel?

Solution:Distance = Speed × Time Distance = 850 km/h × 3.5 h Distance = 2,975 km In miles: 2,975 ÷ 1.609 = 1,849 miles

Result:2,975 km (1,849 miles)

Frequently Asked Questions

How do I calculate speed from distance and time?

Speed = Distance ÷ Time. For example, if you travel 100 km in 2 hours, your speed is 100 ÷ 2 = 50 km/h. Make sure distance and time units are compatible.

How do I convert mph to km/h?

Multiply mph by 1.60934 to get km/h. For example, 60 mph × 1.60934 = 96.56 km/h. To convert km/h to mph, divide by 1.60934.

What's the difference between speed and velocity?

Speed is how fast something moves (scalar, just magnitude). Velocity includes direction (vector). A car going 60 mph in circles has constant speed but changing velocity.

How do I calculate travel time?

Time = Distance ÷ Speed. If you need to travel 300 km at 60 km/h, time = 300 ÷ 60 = 5 hours. Add time for stops, traffic, and rest breaks.

What is a knot?

A knot is one nautical mile per hour, used in maritime and aviation. 1 knot = 1.852 km/h = 1.151 mph. The term comes from counting knots on a rope to measure ship speed.

How do I calculate average speed?

Average Speed = Total Distance ÷ Total Time. If you drive 100 km in 1 hour, stop for 30 min, then drive 50 km in 1 hour, average speed = 150 km ÷ 2.5 h = 60 km/h.

How does speed affect braking distance?

Braking distance increases with the square of speed. Doubling your speed quadruples braking distance. At 60 mph, stopping distance is about 4× what it is at 30 mph.

What's the speed of light?

Light travels at 299,792,458 m/s (about 1.08 billion km/h). Nothing can exceed this speed. It takes light 8 minutes to reach Earth from the Sun.

How do I calculate pace for running?

Pace is time per distance (inverse of speed). If you run 5 km in 25 minutes, pace = 25 ÷ 5 = 5 min/km. To convert, divide 60 by pace to get km/h.

Background & Theory

Speed is the rate of change of position with time. It's one of the most fundamental concepts in physics and essential for transportation, sports, engineering, and everyday life.

Fundamental Formula:
Speed = Distance ÷ Time

Rearrangements:

Distance = Speed × Time
Time = Distance ÷ Speed

Common Speed Units:

Unit	Abbreviation	Conversion
km/h	kph	Base unit
mph	mi/h	× 1.609 = kph
m/s	mps	× 3.6 = kph
knots	kn	× 1.852 = kph
ft/s	fps	× 1.097 = kph

Reference Speeds:

Human walking: 5 km/h
Sprinting: 35 km/h
Cheetah: 120 km/h
Highway driving: 100 km/h
Commercial jet: 900 km/h
Sound (sea level): 1,235 km/h
Earth orbit: 28,000 km/h
Light: 1,079,000,000 km/h

Average vs Instantaneous Speed:

Instantaneous: speed at a specific moment
Average: total distance ÷ total time

History

Speed measurement has evolved dramatically through history. Ancient civilizations estimated travel time by day's journey. The Romans built milestones along roads, enabling crude speed calculations. Galileo Galilei (1564-1642) was among the first to study motion scientifically, using inclined planes to measure acceleration. His work laid groundwork for understanding speed and velocity. The knot originated from 16th-century sailors who used a "chip log" - a rope with evenly spaced knots thrown overboard. Counting knots that passed in a fixed time gave ship speed. The speedometer was invented in 1888 by Croatian Josip Belušić. Early automobile speedometers used centrifugal force with rotating weights. Modern speedometers use vehicle speed sensors and GPS. The speed of sound was first measured accurately by William Derham in 1709. The speed of light was first calculated by Ole Rømer in 1676 by observing Jupiter's moons.