Speed, Distance & Time Calculator
Find any value using the SDT triangle — supports mixed units and shows every step of the working, including unit conversions.
Step-by-step solution
Choose what to find and enter the other two values to see full working.
1 hour = 60 min = 3,600 s • 1 km = 1,000 m
1 km/h ≈ 0.278 m/s • 1 mph ≈ 1.609 km/h
Speed, Distance & Time Calculator Explained
Core concepts, classroom applications, and plain-English explanations for all audiences.
When would you actually use this?
Every car journey uses this triangle. "It's 180 miles to Manchester — if we average 60 mph, how long will it take?" Time = Distance ÷ Speed = 180 ÷ 60 = 3 hours. Average speed cameras on motorways work the same way: they measure distance between two points and divide by your travel time to find your average speed.
Worked example
"You're planning a 240 km road trip. You expect to average 80 km/h. How long will the drive take?"
Formula: Time = Distance ÷ Speed
Time = 240 ÷ 80
Result: 3 hours
Cover T in the SDT triangle — D and S remain, so T = D ÷ S.
Running and cycling pace
Runners track pace in minutes per km (e.g. 5:30/km). This is just time ÷ distance inverted — if you run 10 km in 55 minutes, your pace is 5.5 min/km and your speed is 60 ÷ 5.5 ≈ 10.9 km/h. Cyclists use the same triangle to plan rides and target average speeds.
Mistake to avoid
Mixing units — if distance is in km and speed is in mph, convert first. The SDT triangle only works when distance and speed share consistent units. 1 mile ≈ 1.609 km, 1 hour = 60 minutes.
Speed, Distance, Time Calculator
Understanding the relationship between speed, distance, and time is a fundamental concept in both GCSE Maths and Physics. Whether you're calculating how long a journey will take, how fast something is moving, or how far it has travelled, these three quantities are always linked.
Our calculator helps you quickly find any of these values when you know the other two. It's perfect for checking homework, revising for exams, or just understanding real-world scenarios. The key formulas are: Speed = Distance / Time, Distance = Speed × Time, and Time = Distance / Speed. These are often remembered using the helpful Speed-Distance-Time triangle.
Common mistakes to avoid
- Calculating speed for 10 km in 30 minutes as 10 / 30 = 0.33 km/min:While mathematically correct for km/min, this isn't a standard unit and often leads to errors when comparing or converting. The question usually implies km/h or m/s. Convert minutes to hours first: 30 minutes = 0.5 hours. Then, Speed = 10 km / 0.5 h = 20 km/h.
- Using the wrong formula, e.g., calculating time as Speed × Distance:This is a common mix-up when rearranging the formula. Always refer to the SDT triangle or the base formula (Speed = Distance / Time) to derive the others correctly. Time = Distance / Speed. If you cover the 'T' in the triangle, you're left with 'D' over 'S'.
- Mixing units without converting, e.g., distance in km and speed in m/s:The units must be consistent. If distance is in kilometres and time is in seconds, your speed will be in km/s, which is rarely useful. You need to convert one of them. Convert everything to a consistent set of units before calculating. For example, convert km to metres (1 km = 1000 m) or m/s to km/h.
- Forgetting to convert hours and minutes into a single decimal value for time:If a journey takes '1 hour and 30 minutes', using '1.30' in a calculation is incorrect. 30 minutes is half an hour, not 0.3 of an hour. Convert the minutes part to a decimal of an hour: 30 minutes / 60 minutes = 0.5 hours. So, 1 hour and 30 minutes becomes 1.5 hours.