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Speed Distance Time Calculator

Select what you want to calculate, then enter the two known values. Switch between calculating speed, distance, or time with one click.

Speed

100 km/hkilometres per hour
62.1 mphmiles per hour
27.8 m/smetres per second

Journey time summary

1 hrduration
100 kmdistance

The Speed-Distance-Time Relationship

Speed, distance, and time are three fundamental physical quantities that are always mathematically related. Knowing any two allows you to calculate the third:

Speed = Distance ÷ Time

Distance = Speed × Time

Time = Distance ÷ Speed

This is often taught using the "DST triangle" or "magic triangle" where you cover the quantity you want to find and the remaining two show the operation needed.

Worked Examples

Example 1: Finding Speed

A car travels 240 km in 3 hours. What is its average speed?

Speed = 240 km ÷ 3 hours = 80 km/h

Example 2: Finding Distance

A train travels at 120 km/h for 2.5 hours. How far does it travel?

Distance = 120 km/h × 2.5 hours = 300 km

Example 3: Finding Time

A cyclist rides 45 km at an average speed of 18 km/h. How long does the journey take?

Time = 45 km ÷ 18 km/h = 2.5 hours = 2 hours 30 minutes

Speed Unit Conversions

FromTo km/hTo mphTo m/s
1 km/h10.62140.2778
1 mph1.609310.4470
1 m/s3.62.23691
1 knot1.8521.15080.5144

Common Speed Reference Points

Speedkm/hmphContext
Walking pace53.1Average adult on flat ground
Jogging8–105–6.2Easy running pace
Cycling (casual)15–209–12Recreational cycling
Cycling (fast)30–4019–25Road cycling / commute
City driving30–5019–31Urban speed limits
Highway driving100–13062–81Motorway limits
Speed of sound1,235767At sea level, 20°C
Speed of light1.08 billion671 millionIn vacuum

Pace vs. Speed

In running and cycling, pace is the inverse of speed — it measures how long it takes to cover a unit distance (e.g., minutes per kilometre):

Pace (min/km) = 60 ÷ Speed (km/h)

Speed (km/h)Pace (min/km)5 km time10 km timeMarathon time
6 km/h10:00 min/km50:001:40:007:02:00
8 km/h7:30 min/km37:301:15:005:16:00
10 km/h6:00 min/km30:001:00:004:13:00
12 km/h5:00 min/km25:0050:003:31:00
15 km/h4:00 min/km20:0040:002:49:00

Frequently Asked Questions

How do I calculate average speed for a round trip?

Average speed for a round trip is NOT the simple average of the two one-way speeds. The correct formula is: Average Speed = 2 × Speed1 × Speed2 ÷ (Speed1 + Speed2). For example, driving 60 km/h to a destination and 100 km/h back gives an average speed of 2 × 60 × 100 ÷ (60 + 100) = 75 km/h, not 80 km/h.

What is the difference between speed and velocity?

Speed is a scalar quantity — it only has magnitude (how fast). Velocity is a vector — it has both magnitude and direction. Average speed is total distance divided by total time; average velocity is total displacement (net change in position) divided by total time. For a round trip that returns to the start, average velocity is zero even if average speed is 100 km/h.

How do I convert km/h to m/s?

Divide by 3.6. So 90 km/h = 90 ÷ 3.6 = 25 m/s. Conversely, multiply m/s by 3.6 to get km/h. This works because there are 1000 meters in a km and 3600 seconds in an hour: 1 km/h = 1000 m ÷ 3600 s = 1/3.6 m/s.

Why does time use decimals instead of minutes?

This calculator uses decimal hours (e.g., 1.5 hours = 1 hour 30 minutes) to keep the math simple. In the formula, time must be in the same unit as the rate. If speed is km/h, time must be in hours. The result panel converts decimal hours to hours and minutes for readability.

How do I calculate fuel consumption from speed and distance?

Fuel consumption depends on speed, vehicle type, terrain, and driving style. As a rough guide, most petrol cars are most efficient at 80–90 km/h. Use our Fuel Cost Calculator or Driving Cost Calculator to estimate fuel costs for your journey.

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