How to Calculate Speed, Distance and Time Easily

The Speed-Distance-Time Relationship

Speed, distance, and time are three related quantities in physics. If you know any two of them, you can calculate the third.

The fundamental formula is:

Speed = Distance ÷ Time

Or written as: s = d / t

This can be rearranged to find any variable:

• Distance = Speed × Time → d = s × t
• Time = Distance ÷ Speed → t = d / s

The Formula Triangle

A helpful way to remember all three formulas is the SDT triangle:

Place D at the top, and S and T at the bottom:

D

---

S × T

• Cover the variable you want to find
• What remains shows you the formula:
  • Cover D → S × T (Distance = Speed × Time)
  • Cover S → D/T (Speed = Distance ÷ Time)
  • Cover T → D/S (Time = Distance ÷ Speed)

This triangle is your best friend for speed-distance-time problems.

Calculating Speed

Formula: Speed = Distance ÷ Time

Example 1

A car travels 150 km in 3 hours. What is its speed?

Speed = 150 ÷ 3 = 50 km/h

Example 2

A runner covers 400 meters in 50 seconds. What is their speed?

Speed = 400 ÷ 50 = 8 m/s

Calculating Distance

Formula: Distance = Speed × Time

Example 1

A train moves at 80 km/h for 2.5 hours. How far does it travel?

Distance = 80 × 2.5 = 200 km

Example 2

A cyclist rides at 12 m/s for 30 seconds. How far do they go?

Distance = 12 × 30 = 360 meters

Calculating Time

Formula: Time = Distance ÷ Speed

Example 1

A plane flies 2400 km at 600 km/h. How long does the flight take?

Time = 2400 ÷ 600 = 4 hours

Example 2

A boat travels 45 km at 15 km/h. How long does the trip take?

Time = 45 ÷ 15 = 3 hours

Unit Conversions

The most important thing in speed-distance-time problems is making sure your units are consistent.

Converting km/h to m/s

Multiply by 1000 and divide by 3600 (or divide by 3.6):

• 72 km/h = 72 ÷ 3.6 = 20 m/s
• 36 km/h = 36 ÷ 3.6 = 10 m/s

Converting m/s to km/h

Multiply by 3.6:

• 25 m/s = 25 × 3.6 = 90 km/h
• 5 m/s = 5 × 3.6 = 18 km/h

Converting minutes to hours

Divide by 60:

• 90 minutes = 90 ÷ 60 = 1.5 hours
• 45 minutes = 45 ÷ 60 = 0.75 hours

For more on unit conversions, check out our guide on how to convert units.

Real-World Examples

Example 1: Road trip planning

You need to drive 300 km and want to arrive in 4 hours. What average speed do you need?

Speed = 300 ÷ 4 = 75 km/h

Example 2: Running pace

You run 5 km in 25 minutes. What is your speed in km/h?

First, convert 25 minutes to hours: 25 ÷ 60 = 0.417 hours

Speed = 5 ÷ 0.417 = 12 km/h

Example 3: Average speed for a multi-leg journey

You drive 100 km at 50 km/h, then 150 km at 75 km/h. What is your average speed?

Total distance = 100 + 150 = 250 km Time for leg 1 = 100 ÷ 50 = 2 hours Time for leg 2 = 150 ÷ 75 = 2 hours Total time = 4 hours

Average speed = 250 ÷ 4 = 62.5 km/h

Important: Average speed is total distance ÷ total time — NOT the average of the two speeds!

Practice Problems

1. A bus travels 240 km in 4 hours. What is its speed?
2. A plane flies at 900 km/h for 3 hours. How far does it travel?
3. A person walks 6 km at 4 km/h. How long does the walk take?
4. Convert 108 km/h to m/s.
5. You cycle 15 km at 20 km/h, then 10 km at 25 km/h. What is your average speed?

Answers: (1) 60 km/h (2) 2700 km (3) 1.5 hours (4) 30 m/s (5) 21.4 km/h

Need More Help?

Speed, distance, and time problems come up in physics, math, and real life. Mr Jarven AI Tutor can walk you through any problem, convert units for you, and explain the concepts until they click.

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