How the pace math and the race predictions work
Pace is just time divided by distance. If you know any two of those three numbers, the third is determined. This page does that conversion in US or metric units and also reports speed in miles per hour or kilometers per hour, which is handy when a treadmill is labeled in speed rather than pace.
The race table is a different kind of estimate. It uses the Riegel formula, published in 1977 as a way to scale endurance times: T2 = T1 × (D2 / D1)^1.06. The 1.06 exponent is a typical road-running value, not a personal constant. The table takes the performance you entered — a 5K time, a 10-mile tempo, or a marathon — and scales it to common race distances. A 25-minute 5K, for example, scales to a 10K a little over 52 minutes under this rule.
Riegel predictions assume similar conditions and similar effort. They do not know about hills, heat, a packed start, or whether you trained for 26.2 miles or only for 5K speed. People often run a bit faster than the formula on a shorter race they are specifically sharpened for, and a bit slower on a longer race they have not trained to finish. Treat the table as a planning sketch for goal times, not as a promise.
Splits are even in this model. If your course is rolling or you plan a conservative first half, your actual split sheet should not look perfectly flat. Treadmill pace can be compared with overground pace at the same speed; a common coaching habit is to set a slight treadmill incline when trying to mimic outdoor cost, but this calculator’s pace conversion itself does not add grade. For calories on a belt, use the running and treadmill calorie calculator, which can include incline.
For aerobic capacity estimates from a 12-minute or 1.5-mile run, see the VO2 max calculator. For walking, use the walking calorie calculator rather than forcing a walk into a race-prediction table.
Frequently asked questions
What is a good 5K pace?
There is no single good pace. The useful question is what pace you can hold for that distance on the day, and whether it matches the training you have actually done. Use this page to turn a goal time into a per-mile or per-kilometer number you can check on a watch.
How accurate is the Riegel race predictor?
It is a published rule of thumb, not a physiology lab. It tends to be more reasonable when the two distances are not extremely far apart and when both races are run all-out in similar weather. It is weaker for predicting a marathon from a short time trial if you have not built marathon endurance.
Should I use minutes per mile or minutes per kilometer?
Use whichever your watch and your race are labeled in. Switch the page to metric for min/km and kilometers. The underlying math is the same.
Can I predict a marathon from a recent 5K?
You can see the Riegel number, but you should not treat it as a plan by itself. Marathon performance depends on long-run training, fueling, and heat management that a 5K does not test. If the prediction looks exciting, back it up with training, not with the exponent alone.
Why does my treadmill speed not match the pace I expected?
Some consoles round oddly, and belt calibration can drift. Convert the speed on this page and compare. Also remember that indoor running has no wind and often a different stride; pace can feel easier or harder than the same number outdoors.