Speed, distance, and time are connected by one simple formula triangle. Master it and you can solve any related problem.
The Formula Triangle
Distance = Speed × Time
Speed = Distance / Time
Time = Distance / Speed
Cover the variable you want to find, and the remaining two show the operation:
- Cover D: Speed × Time
- Cover S: Distance / Time
- Cover T: Distance / Speed
Worked Examples
Find distance: Car travels at 60 mph for 2.5 hours:
Distance = 60 × 2.5 = 150 miles
Find speed: Cyclist covers 45 km in 3 hours:
Speed = 45 / 3 = 15 km/h
Find time: Plane flies 1,800 miles at 450 mph:
Time = 1,800 / 450 = 4 hours
Unit Consistency
Always use consistent units. If speed is in km/h, time must be in hours and distance in km.
Converting time units:
- 90 minutes = 1.5 hours (divide by 60)
- 45 minutes = 0.75 hours
Example: Train travels at 120 km/h for 45 minutes:
Time = 45/60 = 0.75 hours
Distance = 120 × 0.75 = 90 km
Average Speed
When speed varies, average speed is total distance divided by total time — NOT the average of the speeds.
Example: Drive 60 mph for 2 hours, then 40 mph for 3 hours:
Total distance = (60×2) + (40×3) = 120 + 120 = 240 miles
Total time = 5 hours
Average speed = 240/5 = 48 mph
(Not (60+40)/2 = 50 mph)
Speed Unit Conversions
| From | To | Multiply by | |------|-----|------------| | mph | km/h | 1.60934 | | km/h | mph | 0.62137 | | m/s | km/h | 3.6 | | km/h | m/s | 0.27778 | | knots | mph | 1.15078 |
Relative Speed
Same direction: Relative speed = Speed 1 - Speed 2
Opposite directions: Relative speed = Speed 1 + Speed 2
Example: Two trains, one at 80 km/h and one at 100 km/h, heading toward each other. They are 360 km apart. When do they meet?
Relative speed = 80 + 100 = 180 km/h
Time = 360/180 = 2 hours
Use our Speed Distance Time Calculator to solve any of the three variables with automatic unit conversion.