Running Pace Calculator
Calculate your pace and predict race times using Riegel's formula
This running pace calculator does two things. First, it converts pace and distance into time, so you can plan a goal time at a target pace (or work backwards from a goal time to required pace). Second, it predicts your times at other distances based on a known time, using the Riegel formula which is the standard exponent-based predictor used by most race-time predictors online.
Useful in practice: you ran a 5K in 25 minutes; the predictor estimates roughly 52 minutes for 10K, 1:55 for a half marathon, and 4:00 for a marathon if your training matches the distance. Note that word if. Marathon predictions from a 5K time assume you have actually trained for the longer distance. A fast 5K runner who has never gone past 8K will not run the predicted marathon time; they will hit the wall around 30K because the limiter shifts from VO2max to glycogen and muscular endurance.
Built and reviewed by Kazi Habib, B.Pharm, MBA, PMP. The deep dive below covers when the predictor is reliable, how the math actually works, and the halal-Canadian race calendar (which exists but is rarely consolidated anywhere).
How this calculator works
The pace calculator uses the basic identity: pace = time / distance, time = pace x distance. Distance can be 1 mile, 5K, 10K, half marathon, marathon, or custom.
The race-time predictor uses the Riegel formula: T2 = T1 x (D2/D1)^1.06. The exponent of 1.06 captures the fact that pace slows nonlinearly with distance (you cannot hold your 5K pace for a marathon; the slowdown is predictable). Riegel was a marathon researcher who fit this formula to a large dataset of race times in the 1970s, and it remains the standard predictor across Strava, McMillan, and most running apps.
When to use this calculator
Use this when you set a target finish time for an upcoming race and need the per-km or per-mile pace to train to, when you ran a recent race and want a realistic prediction for a longer or shorter distance, when you are coaching a less-experienced runner and need to set pace targets for tempo runs and intervals, or when you are training for a marathon and want to verify that your tune-up half-marathon time is on pace for your goal.
When NOT to use this calculator
Skip this if the predicted distance is more than 2x your trained distance. A fast 5K runner has not necessarily trained for marathon endurance; the formula assumes equivalent training adaptation. If you are dealing with significant heat or altitude, pace predictions assume similar conditions to your input race. A 5K time set in 10C will not translate cleanly to a 28C race. If you are coming off injury or a long layoff, the predictor assumes current fitness. If the input distance is under 800m, the formula was fit to longer distances; sprint events are anaerobic-dominated and follow different physiology.
What the result actually means
The predicted times are educated estimates, not guarantees. Marathon predictions specifically should be treated with skepticism unless you have at least 2 to 3 long runs over 30K in the past 6 weeks. The most common failure mode in first marathons is running the first 30K at predicted marathon pace, hitting the wall at 32K, and finishing 20 to 40 minutes slower than predicted. The fitness was real for 30K; the marathon-specific endurance was not.
For race-day pacing strategy, the standard advice is even or negative splits (running the second half at the same pace or slightly faster than the first half). The most common amateur mistake is positive splits driven by adrenaline. The pace calculator can help you set realistic intermediate split targets to keep yourself honest in the first 10K.
Pharmacist take
Running interacts with several medication classes worth knowing. Beta-blockers cap heart rate response, which means heart-rate-based training zones become useless; switch to rate of perceived exertion (RPE) or run by pace. NSAIDs (ibuprofen, naproxen) are popular pre-race and post-race, but chronic NSAID use during heavy training increases kidney injury risk, especially when combined with dehydration. The Canadian Running Magazine and Sports Medicine of Canada both advise against NSAID prophylaxis before long runs. Diuretics for hypertension can cause electrolyte imbalances that catch up to you mid-race; talk to your prescriber about timing relative to long efforts.
The other note: caffeine pre-race is well-evidenced for endurance performance, with the working dose around 3 to 6 mg/kg consumed 30 to 60 minutes before. For a 70 kg adult, that is 210 to 420 mg, or 2 to 4 cups of coffee. More is not better.
Halal, Canadian, and dietary considerations
Halal Canadian race options are less consolidated than I would like, but they exist. Major Canadian races (Scotiabank Toronto Waterfront Marathon, Vancouver Marathon, Calgary Marathon, Servus Edmonton Marathon, Ottawa Race Weekend, Banque Scotia 21K de Montreal) all have varied post-race food options, and water/sports drink on course is uniformly halal-compatible. The trickier question is pre-race carb-loading: most commercial energy gels (GU, Maurten, Honey Stinger) use ingredients that need ingredient-by-ingredient verification, particularly the natural flavours which often use ethanol carriers. Plain Maurten gels are the cleanest from a halal-friendly perspective because the ingredient list is hydrogel, water, and carbohydrates with no flavouring system. Halal-friendly carb-loading at home is easier: white rice, dates, oats, bananas, plain pasta.
For Ramadan-overlapping training (Ramadan in late winter through late spring in 2026-2028 puts it during marathon training season), the practical adjustment is to do long runs in the 2 hours before iftar (so refuel immediately after) and reduce weekday intensity.
Methodology and sources
The Riegel formula and exponent are from Riegel's original race-time prediction work (1977 and 1981 publications). The pace-by-distance physiology framework reflects standard endurance training references including Daniels' Running Formula. Hydration and electrolyte guidance reflects the American College of Sports Medicine position stand on exercise and fluid replacement and Donnelly et al., 2009 ACSM Position Stand on physical activity.
Running Pace FAQ
A comfortable beginner pace is typically 6:00-8:00 minutes per kilometer (or 9:30-13:00 per mile). The key is finding a pace where you can hold a conversation. Speed comes with consistency — most beginners improve significantly in the first 8-12 weeks of regular running.
The most effective approach combines: (1) easy runs at a conversational pace (80% of your training), (2) one tempo or threshold run per week, and (3) one interval session per week. Consistency and gradual increases in weekly mileage matter more than running fast every session.
A tempo run is a sustained effort at your 'comfortably hard' pace — typically your lactate threshold pace. You should be able to speak in short phrases but not hold a full conversation. Tempo runs build the ability to sustain faster paces for longer periods and are a staple of distance training.