What this result means
One-race mode takes distance, finish time, course altitude, and net elevation gain. It divides out the hill multiplier, then the altitude factor, then converts the flat sea-level race time into a marathon with both Daniels VDOT and Riegel. Neither model is primary.
Compare mode runs the same pipeline on race A and race B, then reports which course-adjusted marathon is stronger under each model. Raw VDOT without course adjustments still lives on Compare Two Performances.
A 46:20 10K at sea level with 0 m gain leaves the race clock unchanged, then prints VDOT and Riegel marathon estimates side by side. The same 46:20 at 900 m with 200 m of gain strips both penalties first, so the flat sea-level race time is faster than the watch and the marathon clocks improve.
Compare a slow hilly 10K with a faster flat 10K: after course adjustment the hilly race can win even when the raw clock loses.
Calculation method
Hills first: average grade = net gain ÷ race distance; Minetti 2002 cost ratio undoes the hill multiplier (inverse of elevation-adjusted finish). Altitude next: divide by the Daniels/ACSM-style altitude pace factor (~1% per 300 m above ~600 m). Then VDOT marathon via Daniels and Riegel with exponent 1.06 on the flat sea-level race time.
Deterministic estimate. VDOT and Riegel will usually disagree; both are shown.
Net gain is not a GPS elevation profile. Equal ups and downs are ignored. Heat, humidity, and wind are not modelled. Short GPS courses and bad published gain numbers make fake “improvements.” VDOT and Riegel spread more at slower paces and when you skip course stripping in a hand calculation. Not a ranking.
Frequently asked questions
What is a flat sea-level marathon equivalent?
Your finish time after undoing course hills (Minetti average grade) and altitude, then expressed as an equivalent flat sea-level marathon under VDOT and under Riegel.
Why might this differ from a hand calculation?
This page strips hills and altitude on the distance you raced first, then converts to marathon. Riegel or VDOT applied to the raw watch time skips that step. The two models also disagree by design — both are shown. At slower paces the gap between them and a quick hand estimate can be several minutes even when the math is consistent.
Can I enter altitude and gain in feet?
Yes. Use the M / FT toggle above the altitude and gain fields. Calculations still run in metres internally.
Why both VDOT and Riegel?
They answer the same distance question with different models. Showing both with equal weight makes the disagreement visible instead of hiding it behind one headline.
Should I adjust distance before hills?
No. Average grade uses the distance you raced. This page strips hills and altitude on that distance first, then converts to marathon.
How is this different from Compare Two Performances?
That page compares raw clocks with VDOT (and optional WMA). This page course-adjusts first. Use both when you want raw and course-adjusted votes.