Pace, time, distance, splits, race prediction, heart rate zones, training paces, fueling, hydration, and course adjustments. Enter your numbers and the result updates as you type. Nothing to submit, nothing stored, nothing behind a paywall.
The everyday math of running: converting between pace formats, translating treadmill settings to road effort, and projecting a finish from where you are right now.
Convert a pace between minutes per mile and minutes per kilometer.
Turn a speed in mph or km/h into pace per mile and per kilometer — and back.
Estimate the flat-road pace your treadmill speed and incline are equivalent to. Uses a common effort heuristic; treat it as a guide, not a law.
You're partway through a run or race. Given the distance covered and elapsed time, project your finish at current pace.
Turn a target pace into 400m, 200m, and 100m lap targets for track workouts.
Built on the Riegel endurance formula (T2 = T1 × (D2/D1)k), published by engineer Peter Riegel in 1977. Predictions assume you're trained for the target distance — read how the formula works.
Predict a finish time at any distance from a recent result, with fatigue exponents tuned for road, trail, and ultra racing.
One result, translated across the standard distances (road k = 1.06).
Two common models for predicting the full from your half: Riegel (×2.085) and the coaching rule of doubling plus a cushion.
Bart Yasso's classic workout: your marathon goal in hours:minutes equals your 800m repeat time in minutes:seconds.
Racing well is mostly not going out too fast. Plan even splits, build a negative-split strategy, or find the pace you need over the miles that remain.
A cumulative split table for hitting your goal with metronome pacing.
Run the second half faster than the first. Pick how aggressive the negative split should be.
Mid-race reality check: given where you are and the clock, the pace you need over the remaining distance to hit your goal.
Galloway-style intervals: your overall pace from run and walk segments.
Most training mistakes are pace mistakes — easy days too hard, hard days too easy. These tools set paces from what you can actually race, not what you wish you could.
Easy, marathon, threshold, interval, and repetition paces derived from a recent race using Jack Daniels' VDOT model.
Total time and distance for a repeat session, recoveries included.
Build volume gradually. The old 10% guideline isn't a law of physics, but it's a decent brake.
At a given pace, cadence and stride length trade off against each other. See what your turnover implies.
Zones only work if the numbers underneath them are honest. Estimate max HR, then build zones by percentage of max or by heart rate reserve — read the five zones, explained.
Two published estimates. A field test or lab value beats both — these are population averages with real individual spread.
The classic five-zone model as straight percentages of maximum heart rate.
Zones anchored to your resting HR as well as your max — usually a better fit for trained runners.
Pick an intensity and get the target bpm by both methods.
Estimates of aerobic capacity and the energy cost of running. All of these are models — useful for tracking direction over time, not for judging a single day. More in what VO2 max really means.
Estimate aerobic capacity (Daniels & Gilbert VDOT) from a race you actually ran — usually more useful than a watch's guess.
Run as far as you can in 12 minutes; the distance estimates VO2 max via Cooper's 1968 formula.
A standard estimate of total energy cost: roughly one kilocalorie per kilogram per kilometer. Terrain, pace, and physiology all move the real number.
Body mass index from height and weight. A blunt population statistic — muscular runners routinely read "overweight."
A commonly cited coaching heuristic (~1–2 sec/mile per pound) for how body-weight change affects race pace. It's a rough model — fitness and health come first.
Races longer than about 90 minutes are eating contests you happen to run through. Plan carbs, fluids, and gel timing before the start line — your stomach on mile 20 will not be in a planning mood.
Total carbohydrate for a long run or race. Common targets run 30–60 g/hr for most runners, up to ~90 g/hr with a trained gut and mixed sugar sources.
Total fluid for the duration. Typical intakes fall around 13–27 oz (400–800 ml) per hour, scaled to heat and your own sweat rate.
Weigh yourself before and after a run, track what you drank, and get your personal sweat rate — the number every hydration plan should start from.
A simple gel schedule from your expected finish time and preferred interval.
The course and the weather don't care about your goal pace. These adjustments are honest approximations of well-known effects — use them to set expectations, then run by effort.
Warm air taxes cooling and slows race pace. This uses a common rule of thumb (~1% slower per 5°F above 60°F) — humidity makes it worse.
Thinner air, less oxygen. Roughly a 1% slowdown per 1,000 ft above ~2,000 ft for unacclimated sea-level runners in distance races — an estimate with wide individual variation.
What your pace on a hill is "worth" on the flat, using standard coaching heuristics (uphills cost more than downhills give back).
Estimated time a course's total climb adds versus a flat race, using the Naismith/Scarf equivalence (1,000 ft of gain ≈ 1.5 extra flat miles).
Gear that pairs with the calculators above — fuel for the carb planner, bottles for the fluid planner, a watch for the pace targets. These are Amazon links; each opens a curated search so you can compare current prices and reviews.
Run your numbers in the Carb Fueling Planner, then stock up. Mix brands and flavors before race day.
Live pace, heart rate zones, and splits on your wrist — the field version of every tool on this page.
Carry what the Fluid Planner says you need, especially past the half-marathon distance.
The cheapest performance upgrade in running. Your mile-20 feet will thank you.
Non-negotiable for long runs and hot-weather racing. Apply before you think you need it.
The mileage progression plan only works if your legs recover between weeks.
For dawn miles, dusk miles, and every 100-miler's long night.
Gels, phone, keys — somewhere to put the fueling plan you just calculated.
As an Amazon Associate, calculaterun.com earns from qualifying purchases. Prices and availability are set by Amazon and its sellers.
The math and physiology behind the calculators — written by a runner, for runners.
The 1977 equation behind nearly every race predictor — and where it breaks down.
Why runners think in minutes per mile, and the mental math that makes racing easier.
What each zone trains, how to set them honestly, and why most easy runs are too fast.
The most quoted number in endurance sport — what it measures and what it doesn't.
Cookies & ads. We use cookies for advertising (Google AdSense) and, if enabled, analytics. Choose "Essential only" and no advertising or analytics cookies will be set. See our Privacy Policy.