Race Time Predictor: method, checked example and practical limits
Project an equivalent race time with the Riegel endurance equation. The equivalent performance assumes comparable conditioning and race conditions over the two distances.
Inputs used by this calculator
Race Time Predictor uses the fields below. The starting values reproduce the page example; replace them with values from the same units and time period before using the result.
| Input | Starting example | Accepted value | How it is used |
|---|---|---|---|
| Known distance (km) | 5 | 0.01 to 1000 | Supplies the known distance (km) quantity used by the published equation or result breakdown. |
| Known finish time (minutes) | 25 | 0.01 to 100000 | Supplies the known finish time (minutes) quantity used by the published equation or result breakdown. |
| Target distance (km) | 10 | 0.01 to 1000 | Supplies the target distance (km) quantity used by the published equation or result breakdown. |
| Riegel exponent | 1.06 | 0.5 to 2 | Supplies the riegel exponent quantity used by the published equation or result breakdown. |
Inputs and measurement conventions
The quantities used on this page are Known distance (km), Known finish time (minutes), Target distance (km), Riegel exponent. Start with values for the same situation and read the units attached to each field. The field reference below shows supported choices and numerical limits.
Large extrapolations, especially to a marathon, are sensitive to endurance and fueling. The exponent is adjustable, not a universal personal constant.
Method and equation
Scale a known finish time by the target-to-known distance ratio raised to the selected endurance exponent.
Race Time Predictor uses the following stated relationship: target time = known time × (target distance ÷ known distance)^exponent. Its assumptions determine which question the answer can resolve.
target time = known time × (target distance ÷ known distance)^exponentWorked calculation with the starting values
Known distance (km): 5; Known finish time (minutes): 25; Target distance (km): 10; Riegel exponent: 1.06. These starting values give 52.12328804 predicted finish minutes. The calculation breakdown is Hours: 0; Remaining minutes: 52.12328804; Predicted pace (min/km): 5.212328804; Distance ratio: 2.
A 25-minute 5K predicts about 52.12 minutes for 10K at exponent 1.06.
Reading the answer
The equivalent performance assumes comparable conditioning and race conditions over the two distances.
Hours: 0; Remaining minutes: 52.12328804; Predicted pace (min/km): 5.212328804; Distance ratio: 2. These intermediate quantities make the stated Race Time Predictor model inspectable; they should be read together with the main answer rather than treated as independent guarantees.
Common errors and model boundaries
Large extrapolations, especially to a marathon, are sensitive to endurance and fueling. The exponent is adjustable, not a universal personal constant.
Training, terrain, weather, fatigue and distance specialization can make actual performance substantially different.
Independent verification and next decision
Such an extrapolation is unreliable because the events depend on different performance and endurance characteristics.
For the Race Time Predictor method, compare target time = known time × (target distance ÷ known distance)^exponent with the starting inputs and the calculation table. The linked Vickers and Vertosick: validation of race-time prediction and World Athletics: competition and technical rules references identify the relevant definitions, conventions or domain limitations. Retain intermediate precision when comparing a manually worked answer.
Race Time Predictor worked-example ledger
| Quantity | Example value | Role |
|---|---|---|
| Known distance (km) | 5 | Entered assumption |
| Known finish time (minutes) | 25 | Entered assumption |
| Target distance (km) | 10 | Entered assumption |
| Riegel exponent | 1.06 | Entered assumption |
| Main answer | 52.12328804 predicted finish minutes | Calculated from the starting inputs |
| Hours | 0 | Intermediate or contextual output |
| Remaining minutes | 52.12328804 | Intermediate or contextual output |
| Predicted pace (min/km) | 5.212328804 | Intermediate or contextual output |
| Distance ratio | 2 | Intermediate or contextual output |
Frequently asked questions
Can I predict a marathon from one short sprint?
Such an extrapolation is unreliable because the events depend on different performance and endurance characteristics.
Which relationship does the Race Time Predictor use?
Scale a known finish time by the target-to-known distance ratio raised to the selected endurance exponent. The displayed relationship is target time = known time × (target distance ÷ known distance)^exponent.
What do the starting values produce in the Race Time Predictor?
Known distance (km): 5; Known finish time (minutes): 25; Target distance (km): 10; Riegel exponent: 1.06. These starting values give 52.12328804 predicted finish minutes. The calculation breakdown is Hours: 0; Remaining minutes: 52.12328804; Predicted pace (min/km): 5.212328804; Distance ratio: 2.
How should I interpret this Race Time Predictor answer?
The equivalent performance assumes comparable conditioning and race conditions over the two distances.
Which input mistake most affects the Race Time Predictor?
Large extrapolations, especially to a marathon, are sensitive to endurance and fueling. The exponent is adjustable, not a universal personal constant.
What is outside this Race Time Predictor model?
Training, terrain, weather, fatigue and distance specialization can make actual performance substantially different.
What to keep in mind
Training, terrain, weather, fatigue and distance specialization can make actual performance substantially different.
Results are rounded for display in US format, with money in dollars and cents; CSV exports keep full calculation precision. This is a calculation summary, not an official certificate.