How accurate is the race time predictor?

The Riegel formula is accurate within 2–5% for most runners across distances from 5K to marathon, when the reference effort is a recent, all-out race.

What is the Riegel formula?

The Riegel formula (T2 = T1 × (D2 / D1)^1.06) was published by Pete Riegel in 1977. It models the relationship between race distance and finish time using a fatigue exponent of 1.06.

How do I calculate my running pace?

Divide your total race time in seconds by the distance in kilometres or miles. For example, a 55-minute 10K equals 5:30 per km. ChaseTime calculates this instantly as you type.

What treadmill speed equals a 5:00/km pace?

A 5:00 per km pace equals 12.0 km/h on a treadmill (60 ÷ 5 = 12). Use the Treadmill tab in ChaseTime to convert any pace to km/h or mph instantly.

How do I predict my marathon time from a half marathon?

Enter your half marathon distance (21.1 km) and finish time into ChaseTime's Pace + Races tab. The calculator applies the Riegel formula to project your full marathon finish time.

Why should I add incline on a treadmill?

Running on a treadmill lacks wind resistance. Adding 1–2.5% incline compensates for this difference, making treadmill effort more equivalent to outdoor running at the same pace.

ChaseTime — Running Pace Calculator & Race Time Predictor

📊 Average Times by Age

How to Use This Running Calculator

Pace Calculator

Enter any distance (km or miles) and your finish time to instantly calculate your running pace per kilometre or mile. Works for any distance — track intervals, 5K, 10K, half marathon, or full marathon.

Race Time Predictor

ChaseTime uses the Riegel formula — T2 = T1 × (D2 / D1)^1.06 — to predict how fast you can race at other distances. Used by coaches worldwide to set realistic race goals.

Treadmill Speed Converter

Convert your outdoor running pace (min/km or min/mile) to the treadmill speed setting in km/h or mph. Never do the maths in your head again.

Frequently Asked Questions

How accurate is the race time predictor?: The Riegel formula is accurate within 2–5% for most runners across distances from 5K to marathon, when the reference effort is a recent, all-out race.
What is the Riegel formula?: The Riegel formula (T2 = T1 × (D2 / D1)^1.06) was published by Pete Riegel in 1977. ChaseTime uses the standard exponent of 1.06 for road running.
How do I calculate my running pace?: Divide your finish time by distance — e.g. a 55-minute 10K = 5:30/km. ChaseTime calculates this instantly as you type.
What treadmill speed equals a 5:00/km pace?: 5:00/km = 12.0 km/h (60 ÷ 5 = 12). Use the Treadmill tab to convert any pace instantly.
How do I predict my marathon time from a half marathon?: Enter 21.1 km and your half marathon time. ChaseTime projects your full marathon time using the Riegel formula.