Formulas & Conversions
How to Use
Pick the tab for what you want to find — Time, Speed or Distance.
Fill in the two known values and select their units from the dropdowns.
Click Calculate for an instant result. Use Unit Converter for km/h ↔ m/s.
Frequently Asked Questions
Multiply by 5/18. Example: 72 km/h = 72 × 5/18 = 20 m/s. To convert m/s to km/h, multiply by 18/5.
Speed = Distance ÷ Time = 200 ÷ 10 = 20 m/s = 20 × 18/5 = 72 km/h.
Average Speed = 2ab ÷ (a+b), where a and b are the two speeds. Example: going at 40 km/h and returning at 60 km/h → Average = 2×40×60 ÷ (40+60) = 4800 ÷ 100 = 48 km/h. Note: this is always less than the arithmetic mean (50 km/h here) because more time is spent at the slower speed.
For trains moving towards each other, relative speed = sum of speeds = 60 + 40 = 100 km/h. Time to meet = Distance ÷ Relative Speed = 200 ÷ 100 = 2 hours. For trains moving in the same direction: relative speed = difference of speeds. This "relative speed" concept is a favourite in SSC CGL, RRB NTPC, and IBPS exams — always add speeds when approaching, subtract when same direction.
Total distance to cover = 300 + 200 = 500 m. Time = 50 s. Relative speed = 500/50 = 10 m/s = 10 × 18/5 = 36 km/h. Since relative speed = faster − slower: faster train speed = 36 + 30 = 66 km/h. Train problems always use the sum of lengths as distance, and add speeds (opposite) or subtract (same direction) to get relative speed.