Pace Calculator
Work out running pace, time, or distance from any two of the three. Get pace per km and per mile, speed in km/h and mph, and predicted finish times for the 5K, 10K, half, and full marathon.
- Free, no account
- No watermark
- No usage limit
About the Pace Calculator
The one number this calculator will get wrong for you is the marathon time it predicts from a fast 5K, and every pace tool out there does the same. They take your short-distance pace, stretch it across 42 km as if you never slowed down, and hand back a finish time your legs will never actually run. This tool makes that projection too, because as a starting point it is genuinely useful. The difference is that ours tells you straight, right under the result, that it is a best-case ceiling and not a promise, which most pace tools never bother to say.
The mechanics are simple. Give it any two of the three numbers a runner tracks, distance, time, and pace, and it solves the third instantly. Give it 5 km in 25 minutes and you get a 5:00 per kilometer pace, 8:03 per mile, 12 km/h flat, and it shows all of them at once. Switch it to solve for time instead and it tells you that holding 6:00/km over 10 km puts you across the line at exactly an hour. Works in kilometers or miles, updates the moment you touch a number.
The part I built it around: it never forces you into one unit. Pace comes back in min/km AND min/mile, speed in km/h AND mph, sitting side by side every single time. If you train in metric and then race a course marked in miles, or you are reading a treadmill in km/h off a plan written in min/km, you already know the small misery of doing that conversion in your head at kilometer 18 with your brain half-cooked, so having both columns already there saves you the arithmetic. Look at whichever one matches the markers in front of you and keep running.
No account, no upload, nothing sent anywhere. Every calculation happens in your browser, on your device.
How to use it
- Pick your unit. Kilometers or miles. The distance and pace boxes relabel to match so you never mix systems by accident.
- Choose what to solve for. Tap pace, time, or distance, the one you don't already know. That field grays out, since it is the answer rather than an input.
- Fill in the other two. Distance is a plain number (5, or 3.1). Time and pace are clock values:
mm:ssfor a pace like5:00, andhh:mm:ssfor a longer time like1:45:00. A short run can drop the hours, so25:00reads as 25 minutes. - Or grab a race distance. When you are solving for pace or time, the quick-pick buttons drop in the exact 5K, 10K, half, or marathon distance, so you don't have to remember a half is 21.0975 km.
- Read the rest. The answer sits on top. Below it: pace per km, pace per mile, speed in both units, and predicted finish times for all four standard races at that pace.
Clear any box and the results wait until you have two valid numbers again, with no error screens and no NaN.
Why the predicted marathon time flatters you
The predictions all assume one thing, that you hold the exact same pace from the first step to the last. That is a clean even-effort model, and over short distances it is close to true. A strong runner really can hold near-constant pace through a 5K. Stretch the same assumption across a marathon and it overstates the finish you will actually run, because fatigue, glycogen depletion, and the wall that hits around 30 to 32 km all drag your later kilometers slower than your early ones. Your real marathon pace is meaningfully softer than your 5K pace, never equal to it.
For a truer long-distance estimate, coaches use Riegel's formula: T2 = T1 × (D2 / D1)^1.06. The 1.06 exponent is what accounts for fatigue, it adds time as the distance grows rather than holding pace flat. Run a 25:00 5K and the naive same-pace math predicts a 3:30 marathon. Riegel, accounting for the fade, lands closer to 4:00, and the truth usually sits nearer Riegel. So treat this tool's longer predictions as the ceiling you would hit on a perfect day, fully trained for that distance, and set your actual goal a bit slower. The shorter the gap between your test race and your target, the truer the projection, which is why extrapolating a marathon from a single quick parkrun is the classic way to blow up at halfway.
Pace, speed, and the treadmill problem
Speed and pace are two ways of stating the same thing. Speed is ground covered per unit of time, the km/h or mph on a car dashboard, where a bigger number is quicker. Pace is the flip of that, the minutes it takes to cover one kilometer or mile, so with pace a low number is the fast one. Runners lean on pace because it maps to how a run is planned and felt. Tell yourself to hold 5:30s and you know exactly what each kilometer should cost.
This matters most on the treadmill, which almost always shows speed while your plan is written in pace. The math is 60 divided by your speed in km/h, so 10 km/h is a 6:00/km pace, 12 km/h is 5:00/km, and 8 km/h is a 7:30/km jog. A treadmill at 0% incline is a touch easier than flat outdoor ground because nothing is pushing back on you, so plenty of runners nudge the belt to 1% to match real effort.
Frequently asked questions
How do I work out my pace by hand?
Divide total time by distance. Ten kilometers in 50 minutes is 5:00 per kilometer. The catch is that running times are in mm:ss, not decimal minutes, so 50:30 is not "50.5," it is 3,030 seconds. Convert to seconds, divide by the distance, then convert back to mm:ss. That final conversion is the step people fumble when they are tired, which is exactly the bit the calculator takes off your hands.
What is a good pace for a beginner?
There is no single number, but a sustainable easy range for a new runner is roughly 6:00 to 8:00 per kilometer, about 9:40 to 12:50 per mile. A better test than any number: if you can hold a conversation while you run, the effort is right. Most beginners run their easy days too hard and stall out. Build the habit at a talkable pace and the numbers drop on their own over a few weeks.
Should I set my marathon goal from a 5K time?
Only loosely. Base it on your closest recent race instead. A half marathon or even a 10K sits much nearer to 42 km than a 5K does, so the projection carries far less error. Feed that result into the tool, then set your goal a touch slower than the marathon time it hands back.
What are even and negative splits?
An even split is running every segment at the same pace. A negative split is running the second half faster than the first. Nearly every distance record is set on an even or negative split, because going out too fast (a positive split) burns your glycogen early and you pay for it hard in the closing kilometers. The popular myth is that early fast kilometers "bank" time. They don't, the late slowdown costs more than the early gain, so find your target pace here and hold it or a touch slower through the first few kilometers.
Why does my watch show a different pace than this?
Your GPS watch shows instant pace, your speed over the last second or two, and it jumps around constantly as your stride changes and the satellite signal wobbles. This calculator gives average pace, total time divided by total distance, which is the single number that actually describes the run. Ten kilometers in 50 minutes averages 5:00/km even if the watch swung between 4:30 and 5:40 the whole way. Race and training targets are set on the average, so that is the one to plan around.
Does anything I type get sent anywhere?
No. Every calculation runs in your browser, on your device, and nothing is uploaded, stored, or logged. Your times and paces never leave the screen, which is also why the result appears the instant you type, there is no server to wait on. Once the page has loaded it keeps working with no connection at all.