Speed, Distance & Time Calculator

Calculate speed, distance, or time with the SDT triangle method. Includes unit conversions (km/h ↔ m/s) and step-by-step working for PSLE students!

Calculate Speed, Distance & Time

Select what you want to find, enter your values with units, and see the step-by-step solution.

Speed, Distance & Time Calculator

Cover what you want to find. The remaining shows the formula!

Cover S → D ÷ T

What do you want to calculate?

Distance

Time

The SDT Triangle: Your Best Friend

The SDT Triangle is the easiest way to remember the three formulas for speed, distance, and time.

How It Works

      D
    ─────
    S × T

To find any value, cover it with your finger:

Cover	You See	Formula
D (Distance)	S × T	Distance = Speed × Time
S (Speed)	D ÷ T	Speed = Distance ÷ Time
T (Time)	D ÷ S	Time = Distance ÷ Speed

💡 Memory Trick

Think of Donald Sells Tacos:

Donald is on top (Distance)
Sells and Tacos multiply at the bottom (Speed × Time)

The Three Core Formulas

1. Speed = Distance ÷ Time

$\text{Speed} = \frac{\text{Distance}}{\text{Time}}$

Units: If distance is in km and time is in hours → speed is in km/h

2. Distance = Speed × Time

$\text{Distance} = \text{Speed} \times \text{Time}$

Example: 60 km/h × 2 h = 120 km

3. Time = Distance ÷ Speed

$\text{Time} = \frac{\text{Distance}}{\text{Speed}}$

Example: 150 km ÷ 50 km/h = 3 h

Unit Conversions: The Tricky Part

PSLE loves to mix units! Here’s how to convert them.

Distance Conversions

From	To	Multiply by
km	m	× 1000
m	km	÷ 1000

Time Conversions

From	To	Multiply by
hours	minutes	× 60
minutes	hours	÷ 60
hours	seconds	× 3600
seconds	hours	÷ 3600
minutes	seconds	× 60

Speed Conversions (IMPORTANT!)

Conversion	Formula	Shortcut
km/h → m/s	× 1000 ÷ 3600	÷ 3.6
m/s → km/h	× 3600 ÷ 1000	× 3.6
km/h → m/min	× 1000 ÷ 60	× 16.67

⚠️ PSLE Favourite: km/h ↔ m/s

Memorize this:

km/h to m/s: divide by 3.6
m/s to km/h: multiply by 3.6

Example: 72 km/h = 72 ÷ 3.6 = 20 m/s

Why Does ÷ 3.6 Work?

$\frac{\text{km}}{\text{h}} = \frac{1000 \text{ m}}{3600 \text{ s}} = \frac{1000}{3600} \text{ m/s} = \frac{1}{3.6} \text{ m/s}$

So to convert km/h to m/s, divide by 3.6!

Worked Examples

Example 1: Find Speed

Problem:

A car travels 180 km in 3 hours. Find its speed.

Using the SDT Triangle: Cover S, you see D ÷ T

$\text{Speed} = \frac{\text{Distance}}{\text{Time}} = \frac{180 \text{ km}}{3 \text{ h}} = 60 \text{ km/h}$

Answer: 60 km/h

Example 2: Find Distance with Unit Conversion

Problem:

A cyclist travels at 15 km/h for 45 minutes. How far does she travel?

Step 1: Convert time to hours

$45 \text{ min} = 45 \div 60 = 0.75 \text{ h}$

Step 2: Use the formula

$\text{Distance} = \text{Speed} \times \text{Time} = 15 \times 0.75 = 11.25 \text{ km}$

Answer: 11.25 km

Example 3: Find Time (Answer in Hours and Minutes)

Problem:

A bus travels 140 km at 40 km/h. How long does the journey take?

Using the formula:

$\text{Time} = \frac{\text{Distance}}{\text{Speed}} = \frac{140}{40} = 3.5 \text{ h}$

Convert to hours and minutes:

$3.5 \text{ h} = 3 \text{ h } 30 \text{ min}$

Answer: 3 h 30 min (or 3.5 hours)

Example 4: Speed Conversion

Problem:

Convert 90 km/h to m/s.

Method 1: Using the shortcut

$90 \text{ km/h} = 90 \div 3.6 = 25 \text{ m/s}$

Method 2: Step by step

$90 \text{ km/h} = 90 \times 1000 \text{ m/h} = 90000 \text{ m/h}$

$90000 \text{ m/h} = 90000 \div 3600 \text{ m/s} = 25 \text{ m/s}$

Answer: 25 m/s

Average Speed: A Common Trap!

❌ The #1 Average Speed Mistake

Average speed is NOT the average of two speeds!

Wrong: A car goes 40 km/h then 60 km/h. Average = (40+60)÷2 = 50 km/h ❌

Right: Average Speed = Total Distance ÷ Total Time ✓

The Correct Formula

$\text{Average Speed} = \frac{\text{Total Distance}}{\text{Total Time}}$

Example 5: Average Speed

Problem:

John cycles 20 km at 10 km/h, then cycles another 20 km at 20 km/h. What is his average speed?

Step 1: Find total distance

Total distance = 20 + 20 = 40 km

Step 2: Find time for each part

Time for first part = 20 ÷ 10 = 2 h Time for second part = 20 ÷ 20 = 1 h

Step 3: Find total time

Total time = 2 + 1 = 3 h

Step 4: Calculate average speed

$\text{Average Speed} = \frac{40 \text{ km}}{3 \text{ h}} = 13.33 \text{ km/h}$

Note: The answer is NOT 15 km/h (which would be the average of 10 and 20)!

Common PSLE Mistakes to Avoid

❌ Mistake 1: Mismatched Units

If speed is in km/h, time must be in hours!

Speed = 60 km/h, Time = 30 min → Convert: 30 min = 0.5 h
Then: Distance = 60 × 0.5 = 30 km ✓

❌ Mistake 2: Wrong Formula

Use the SDT triangle! Cover what you want to find.

Want Distance? Cover D → See S × T
Want Speed? Cover S → See D ÷ T
Want Time? Cover T → See D ÷ S

❌ Mistake 3: Converting Hours Wrongly

2.5 hours ≠ 2 h 50 min
2.5 hours = 2 h 30 min (0.5 × 60 = 30 min)

❌ Mistake 4: Average Speed Error

Never average the speeds! Always use: $\text{Average Speed} = \frac{\text{Total Distance}}{\text{Total Time}}$

Quick Reference Card

Formulas

Find	Formula
Speed	S = D ÷ T
Distance	D = S × T
Time	T = D ÷ S
Average Speed	Total D ÷ Total T

Unit Conversions

Conversion	How
km → m	× 1000
m → km	÷ 1000
h → min	× 60
min → h	÷ 60
km/h → m/s	÷ 3.6
m/s → km/h	× 3.6

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