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Running Calculators
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.
Pace Calculator
Pace & Time
Category 1 of 8The everyday math of running: converting between pace formats, translating treadmill settings to road effort, and projecting a finish from where you are right now.
Pace Unit Converter
Convert a pace between minutes per mile and minutes per kilometer.
Speed ↔ Pace
Turn a speed in mph or km/h into pace per mile and per kilometer — and back.
Treadmill Pace Converter
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.
Projected Finish Time
You're partway through a run or race. Given the distance covered and elapsed time, project your finish at current pace.
Track Lap Splits
Turn a target pace into 400m, 200m, and 100m lap targets for track workouts.
Race Prediction
Category 2 of 8Built 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.
Riegel Race Predictor
Predict a finish time at any distance from a recent result, with fatigue exponents tuned for road, trail, and ultra racing.
Equivalent Race Times
One result, translated across the standard distances (road k = 1.06).
Half → Marathon Predictor
Two common models for predicting the full from your half: Riegel (×2.085) and the coaching rule of doubling plus a cushion.
Yasso 800s
Bart Yasso's classic workout: your marathon goal in hours:minutes equals your 800m repeat time in minutes:seconds.
Splits & Strategy
Category 3 of 8Racing 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.
Even Splits Generator
A cumulative split table for hitting your goal with metronome pacing.
Negative Split Planner
Run the second half faster than the first. Pick how aggressive the negative split should be.
Required Pace to Goal
Mid-race reality check: given where you are and the clock, the pace you need over the remaining distance to hit your goal.
Run/Walk Calculator
Galloway-style intervals: your overall pace from run and walk segments.
Training
Category 4 of 8Most 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.
Training Pace Calculator
Easy, marathon, threshold, interval, and repetition paces derived from a recent race using Jack Daniels' VDOT model.
Interval Workout Calculator
Total time and distance for a repeat session, recoveries included.
Weekly Mileage Progression
Build volume gradually. The old 10% guideline isn't a law of physics, but it's a decent brake.
Cadence & Stride Length
At a given pace, cadence and stride length trade off against each other. See what your turnover implies.
Heart Rate
Category 5 of 8Zones 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.
Max Heart Rate Estimator
Two published estimates. A field test or lab value beats both — these are population averages with real individual spread.
Heart Rate Zones (% of Max)
The classic five-zone model as straight percentages of maximum heart rate.
Karvonen Zones (HR Reserve)
Zones anchored to your resting HR as well as your max — usually a better fit for trained runners.
Target Heart Rate
Pick an intensity and get the target bpm by both methods.
Fitness & Body
Category 6 of 8Estimates 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.
VO2 Max from a Race
Estimate aerobic capacity (Daniels & Gilbert VDOT) from a race you actually ran — usually more useful than a watch's guess.
Cooper 12-Minute Test
Run as far as you can in 12 minutes; the distance estimates VO2 max via Cooper's 1968 formula.
Calories Burned Running
A standard estimate of total energy cost: roughly one kilocalorie per kilogram per kilometer. Terrain, pace, and physiology all move the real number.
BMI Calculator
Body mass index from height and weight. A blunt population statistic — muscular runners routinely read "overweight."
Body Weight & Race Pace
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.
Fuel & Hydration
Category 7 of 8Races 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.
Carb Fueling Planner
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.
Fluid Planner
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.
Sweat Rate Calculator
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.
Gel Timing Planner
A simple gel schedule from your expected finish time and preferred interval.
Course & Conditions
Category 8 of 8The 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.
Heat Pace Adjustment
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.
Altitude Adjustment
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.
Grade-Adjusted Pace
What your pace on a hill is "worth" on the flat, using standard coaching heuristics (uphills cost more than downhills give back).
Elevation Gain Time Cost
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).
Recommended Gear
Runner-tested categoriesGear 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.
Energy Gels →
Run your numbers in the Carb Fueling Planner, then stock up. Mix brands and flavors before race day.
GPS Running Watches →
Live pace, heart rate zones, and splits on your wrist — the field version of every tool on this page.
Hydration Vests & Bottles →
Carry what the Fluid Planner says you need, especially past the half-marathon distance.
Anti-Blister Socks →
The cheapest performance upgrade in running. Your mile-20 feet will thank you.
Anti-Chafe Balm →
Non-negotiable for long runs and hot-weather racing. Apply before you think you need it.
Foam Rollers & Recovery →
The mileage progression plan only works if your legs recover between weeks.
Headlamps & Visibility →
For dawn miles, dusk miles, and every 100-miler's long night.
Running Belts →
Gels, phone, keys — somewhere to put the fueling plan you just calculated.
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