Advanced options
The classic triangle: speed = distance / time, distance = speed x time, time = distance / speed. Keep the units consistent and the triangle never lies.
What The Speed Distance Time Calculator Works Out
- Answer: whichever of the three you ask for, from the other two. Speed equals distance over time; rearranging gives distance as speed times time and time as distance over speed. 120 miles at 60 mph is 2 hours; 150 miles in 2.5 hours is 60 mph.
- Formula used: the line of working, with time shown in hours, because the unit trap accounts for most wrong answers: 45 minutes enters the formula as 0.75 hours, not 45 or 0.45. The exam-hall memory aid is the triangle with D on top and S and T below; cover the one you want and the layout shows the operation.
- Average speed: total distance over total time, not the average of the speeds. Drive somewhere at 30 mph and back at 60 mph and the average is 40, not 45, a favourite of every maths paper.
- Breaks and stops (advanced): adds rest stops to a journey time, strips them out of a measured time to show your true moving speed, or shows how far you really travel when stops come out of a fixed time. On a long drive the Highway Code suggests a 15-minute break every two hours.
- Pace (advanced): the same speed expressed as minutes and seconds per mile and per kilometre, the way runners and cyclists think. 10 km/h is a 6:00 per km or 9:39 per mile pace; a 4-hour marathon needs about 9:09 per mile.
- Speed in other units (advanced): mph to km/h (multiply by 1.609), metres per second (divide km/h by 3.6) and knots (nautical miles per hour, 1.852 km). Handy for treadmills that display km/h, European limits in km/h and wind or boat speeds in knots.
- Arrival time (advanced): enter a departure time and get the clock time you arrive, including any breaks, with a note if it rolls past midnight. A quick sanity check against a satnav ETA.
- Speed conversion table (advanced): common speeds side by side in mph, km/h, m/s and pace per mile and per kilometre, in whichever unit you are working in.
- Beyond the classroom: the triangle generalises to any rate, from flow rates and data transfer to work done, which is why it is the single most reused piece of school maths.