Two ways in
Start from a pace, or start from a finish time.
Some runners already know the pace they want to hold. Others only know the time they want on the clock. The calculator accepts either. Set minutes and seconds per kilometer or per mile and the finish times fill in. Or type a goal finish time for 5K, 10K, half marathon or marathon, and the pace required to hold it is solved back from the distance. There is no Calculate button. Every number updates as you type.
The kilometer and mile toggle changes every figure on the page at once, including the column headers, the finish-time rows and the split table. Nothing is left in the other unit, so you are not holding two systems in your head while reading. That matters more than it sounds. A conversion done quickly in the minutes before a start is an easy way to commit to a pace you did not intend.
- Enter a pace in minutes and seconds, per kilometer or per mile
- Or enter a goal finish time for 5K, 10K, half marathon or marathon
- Switch units and every number on the page follows
- Results update as you type, with no Calculate button
The effort columns
The columns show what a change in speed is actually worth.
The finish-time table is not one column. Distances run down the left, on a ladder that runs from 400 m and 800 m through the common kilometer and mile markers up to the marathon, with 5K, 10K, half marathon and marathon called out as rows of their own. Across the top are six efforts scaled against your target speed: 90 percent, 95 percent, target, 105 percent, 110 percent and 115 percent. Each header carries the pace that column represents, so pace and time are read together.
The percentages are of speed, not of pace, which is why the pace steps are not evenly spaced. Speed and pace are reciprocals. Running at 110 percent of a target speed does not make your pace 10 percent quicker, it makes it about 9 percent quicker, because 1 divided by 1.1 is 0.909. Working in speed keeps the columns comparable and makes the true size of a small change obvious, which is usually the part worth knowing.
That is the real use of a wide table. A runner deciding between two paces rarely needs a prediction. They need to see what ten seconds per kilometer costs or buys across the distance they are actually racing, and whether that difference is worth the risk of a faster first half. Reading the columns side by side turns a vague ambition into a decision you can make before the start line, while you can still change your mind.
- A ladder of rows from 400 m and 800 m up to the marathon
- 5K, 10K, half marathon, marathon and common mile distances as their own rows
- Six columns at 90, 95, 100, 105, 110 and 115 percent of target speed
- Each column header shows the pace it represents
Splits
Even splits and negative splits are two different plans.
Below the finish-time table is a split table for the race distance you selected. It lists cumulative elapsed time at each kilometer or mile, so you are reading the number your watch will show as you pass the marker, not the time for that segment alone. Cumulative is the form that is useful mid-race. It is also the form that is hardest to work out in your head once you are tired and the arithmetic stops being free.
Two variants are shown. The even split holds one pace from start to finish and divides the goal time into equal parts. The negative split runs the first half slightly slower than target and the second half slightly faster, arriving at the same finish time by a different route. Neither is inherently correct. The even split is simpler to execute and easier to check. The negative split leaves more room if the day turns out warmer, hillier or harder than expected.
You do not need the whole table on race day. The halfway number and one or two checkpoints may be all you use, and that is enough. Carrying a column of numbers you will not look at is not a pacing strategy. Choose the markers you know you will pass, decide in advance what each one should read, and decide now what you will do if the number comes up slow. That last decision is the easiest one to skip.
- Cumulative elapsed time at every kilometer or mile of the race
- An even-split variant that holds one pace throughout
- A negative-split variant that finishes faster than it starts
- Both variants land on the same goal finish time
What the table is not
Constant-speed arithmetic is a pacing tool, not a prediction.
Every finish time here is straight-line arithmetic. Time equals distance divided by speed, held constant for the whole distance. That is exactly what you want when planning a pace. It is not what happens in a race. A runner who covers 5K at a given pace will not hold that same pace for a marathon. Sustainable speed falls as distance rises, and the drop is large enough that reading one column across distances will flatter you badly at the long end.
Models that estimate the decline exist. Riegel's endurance-time formula, published in 1981, scales a predicted time by the ratio of the distances raised to a fatigue exponent, commonly taken as 1.06. It is a rough fit, calibrated on race results in general rather than on you, and it degrades when the two distances are far apart or the training behind them is uneven. This calculator applies no such model. It reports what constant speed gives, and leaves the fade to your judgment.
Use the table the way it is built to be used. Pick a pace you have evidence you can hold for the distance in front of you, then read the splits for that pace. Evidence means recent training at or close to that effort, over comparable terrain, in comparable conditions. A pace you have only held for two kilometers is a hypothesis. The table will still print a marathon time for it, and that does not make the pace sustainable.
After the calculator
A goal pace is a question about your training.
The number that comes out of a pace calculator is only as good as the training behind it. If a target pace feels arbitrary, that usually means the training has not yet been built to support it. The gap between the pace you want and the pace you can hold tends to narrow over months of structured work: base volume, sustained efforts near threshold, long runs, and enough recovery to absorb the load. Choosing a friendlier column does not close it.
RunPT is a personal running coach for iPhone. It builds a personalized plan for a 5K, 10K, half marathon or marathon goal, tells you what to run each day, and evaluates the runs you sync from COROS, Polar, Suunto or Apple Health. When that training materially changes what should come next, RunPT can update upcoming sessions. A compatible running watch, or Apple Watch data through Apple Health, is needed. Web signups get a 14-day free trial, no payment required.
RunPT provides training guidance, not medical advice, diagnosis, injury treatment or clinical nutrition advice. Pace targets interact with health in ways software cannot see. If something hurts, if a pace that used to be easy has become hard for no clear reason, or if you are returning from illness or injury, that is a conversation for an appropriately qualified professional rather than a column in a table.
- Phased plans for 5K, 10K, half marathon and marathon goals
- Phases: Maintain, Base, Build, Peak, Taper, Recovery
- Activity import from COROS, Polar, Suunto and Apple Health
- A 14-day free trial on web signup, no payment required
FAQ
Pacing questions, answered.
How pace, speed and finish time relate, and where the arithmetic stops being useful.
01What is a running pace calculator?
A running pace calculator converts between pace, distance and time, so that fixing any two of them gives you the third. Enter a pace per kilometer or per mile and it returns the finish time for any distance. Enter a goal finish time for a race and it returns the pace required to hold it. The arithmetic is simple division. Doing it reliably in your head, in the units you race in, under fatigue, is not.
02How do I calculate my running pace?
Divide your total time by the distance you covered. A 50 minute 10K is 3000 seconds divided by 10 kilometers, which is 300 seconds, or 5:00 per kilometer. For miles, divide by 6.214 instead, giving about 8:03 per mile. Convert the time to seconds before dividing and back to minutes and seconds afterwards, because a clock reading is not a decimal number and dividing it as one gives the wrong answer.
03What pace do I need for a 4 hour marathon?
A 4 hour marathon requires 5:41 per kilometer, or 9:09 per mile, held for the full 42.195 km. That is 14400 seconds divided by 42.195, which gives 341 seconds per kilometer. Other common targets work out at 4:16 per km for a 3 hour marathon, 4:59 for 3:30, and 7:07 for 5 hours. Each is an average, so any kilometer run faster than target has to be paid for somewhere later.
04Why are the effort columns percentages of speed rather than pace?
Percentages of speed keep the columns consistent, because pace and speed are reciprocals rather than the same quantity scaled. Running at 110 percent of a target speed produces a pace about 9.1 percent faster, not 10 percent, since 1 divided by 1.1 is 0.909. If the columns stepped by percentages of pace instead, equal-looking steps would represent unequal changes in effort at different points in the table. Working in speed makes a 5 percent step mean the same thing everywhere.
05Should I run even splits or a negative split?
Even splits are the simpler plan and easier to check mid-race, because every kilometer should read the same. A negative split, running the second half slightly faster than the first, is a hedge against starting too hard, which is a common way a goal time is lost. Neither is inherently correct. The choice matters much less than picking a target your training supports, because an over-ambitious even split and an over-ambitious negative split end the same way.
06Can a pace calculator predict my race time?
Not on its own. A pace calculator holds speed constant, so it tells you what a given pace produces over a given distance, which is arithmetic rather than prediction. Sustainable speed falls as distance rises, so a pace held for 5K will not hold for a marathon. Prediction models such as Riegel's 1981 endurance-time formula attempt to estimate that decline, but they are fitted to race results in general rather than to your training, and they lose accuracy across large distance gaps.
07How do I convert pace per km to pace per mile?
Multiply your pace per kilometer by 1.609 to get pace per mile, and divide by 1.609 to go the other way. Convert to seconds first. A 5:30 per km pace is 330 seconds, times 1.609 gives 531 seconds, which is 8:51 per mile. The common error is treating the clock reading as a decimal: 5.30 multiplied by 1.609 gives about 8:32, roughly twenty seconds a mile wrong, and that error compounds over a marathon.
08What is goal pace and how do I choose one?
Goal pace is the average speed required to finish a chosen distance in a chosen time. Choosing one well means grounding it in recent evidence rather than ambition. Useful evidence includes a race at a nearby distance in the last few months, sustained tempo or threshold sessions at or close to the target, and long runs over comparable terrain. If you have not held the pace for a meaningful portion of the race distance in training, treat it as an experiment rather than a plan.
09Why does the table include 400 m and 800 m?
Short rows make the table usable during interval sessions, not only on race day. If a workout calls for 8 by 400 m at 10K effort, the table already shows what each repetition should take at that pace, and what it becomes one column faster or slower. The same applies to 800s, kilometer repeats and mile repeats. Reading rep targets from the same table as your race splits keeps the session and the goal in the same units.
10Do I need the RunPT app to use this pace calculator?
No. The calculator works on its own in the browser, with nothing to install. RunPT is a separate product: a personal running coach for iPhone that builds a personalized plan for a 5K, 10K, half marathon or marathon goal and tells you what to run each day. It evaluates the runs you sync from COROS, Polar, Suunto or Apple Health and can update upcoming training when they materially change what should come next. Web signups get a 14-day free trial, no payment required.
Sources and verification
- NIST Guide for the Use of the International System of Units (SP 811)The exact conversion behind the kilometer and mile toggle: one international mile is 1609.344 meters.