Speed Calculator
Speed Formula
Distance
D = Speed × Time
Time
T = Distance ÷ Speed
Speed Conversions
Related Calculators
Understanding Speed, Distance, and Time
The Speed Formula
Speed, distance, and time are related by a simple formula. If you know any two of these values, you can calculate the third.
Common Speeds
| Object/Activity | mph | km/h | m/s |
|---|---|---|---|
| Walking | 3 | 4.8 | 1.3 |
| Running | 6-8 | 10-13 | 2.7-3.6 |
| Cycling | 12-18 | 19-29 | 5.4-8 |
| City Driving | 25-35 | 40-56 | 11-16 |
| Highway Driving | 55-75 | 89-121 | 25-34 |
| Commercial Airplane | 500-600 | 800-965 | 223-268 |
| Speed of Sound | 767 | 1,234 | 343 |
Example Problems
Finding Speed
Q: You drive 150 miles in 2.5 hours. What's your average speed?
A: 150 ÷ 2.5 = 60 mph
Finding Distance
Q: You drive at 65 mph for 4 hours. How far do you travel?
A: 65 × 4 = 260 miles
Finding Time
Q: You need to travel 200 miles at 50 mph. How long will it take?
A: 200 ÷ 50 = 4 hours
Unit Conversion
Q: Convert 100 km/h to mph.
A: 100 × 0.621 = 62.1 mph
Speed vs. Velocity
Speed is a scalar quantity—it only tells you how fast something is moving. Velocity is a vector quantity—it includes both speed AND direction. For everyday calculations like travel time, speed is sufficient. Physics problems often require velocity to account for direction.
Practical Tips
- Add 10-15% to calculated travel time for stops and traffic
- Average speed is usually lower than cruising speed due to stops
- GPS estimated arrival times factor in current traffic conditions
- Fuel efficiency typically peaks at 45-65 mph for most vehicles
Frequently Asked Questions
How do I calculate speed from distance and time?
Divide distance by time: Speed = Distance / Time. If you travel 120 miles in 2 hours, your average speed is 120 / 2 = 60 mph. Make sure distance and time units match your desired speed unit.
How do I convert mph to km/h?
Multiply mph by 1.609 to get km/h. To convert km/h to mph, multiply by 0.621. Quick reference: 60 mph = 97 km/h, 100 km/h = 62 mph.
What is the difference between speed and velocity?
Speed is just how fast you're moving (a scalar - magnitude only). Velocity includes both speed and direction (a vector). Driving 60 mph north is a velocity; driving 60 mph is a speed.
How do I calculate arrival time for a trip?
Divide distance by speed to get time: Time = Distance / Speed. A 240-mile trip at 60 mph takes 240/60 = 4 hours. Add 15-20% for stops, traffic, and real-world conditions.