Pace Calculator

Four calculators sit above. The first finds any one of pace, time or distance from the other two. The multipoint calculator breaks a run into sections and shows how your pace held up across them. The converter moves a pace between eight units, and the finish time calculator projects where you will end up from where you are now.

All of them work for running, walking, cycling, swimming or anything else measured in distance over time. Placeholder zeros are optional throughout: 5 minutes 3 seconds can be typed as 5:3.

What pace is, and why it is not speed

Pace and speed describe the same thing upside down. Speed is distance over time, as in 5.95 kilometres per hour. Pace is time over distance, as in 10:05 per kilometre. Runners use pace because races are fixed distances, so time per kilometre multiplies straight into a finish time. Cyclists use speed because their rides are open-ended.

Both appear in the result panel, which is worth understanding when a treadmill shows one and your watch shows the other. A 50:25 effort over 5 km is 10:05 per kilometre, 16:13.65 per mile, 5.95 km/h, 3.7 mph, 99.17 metres per minute and 1.65 metres per second. Identical effort, six different numbers.

The mile-to-kilometre conversion is where most arithmetic errors creep in. One mile is 1.609344 kilometres, so a per-mile pace is always a larger number than the per-kilometre pace for the same runner, by about 61%. A 5:00/km pace is 8:03/mile, not 8:00.

Using the three modes

Pace takes a time and a distance and returns how fast you were going, along with the finish time that pace would produce at every common race distance. This is the mode for working out what a training run actually means.

Time takes a distance and a target pace and returns the finish time. This is race planning: pick the pace you believe you can hold and see what it delivers.

Distance takes a time and a pace and returns how far you would get. Useful for time-boxed sessions: how far is 45 minutes at an easy pace?

The event picker fills the distance field with an exact figure. A marathon is 42.195 km, or 26 miles 385 yards, and a half is 21.0975 km. Using 42 or 26 as a shortcut looks harmless and costs about a minute of predicted finish time at most amateur paces.

Splits and even pacing

The splits table lists the clock time you should see at each kilometre and each mile if you hold pace exactly. Printing those or writing them on your arm is still the simplest race strategy there is.

The cumulative chart is deliberately a straight line, because perfectly even pacing is a straight line. Real races bend it. Most recreational runners go out too fast and fade, producing a curve that steepens in the second half, and the time lost in the fade is usually larger than the time gained early. Even or slightly negative splits (running the second half marginally faster) is how nearly every distance world record has actually been set.

The multipoint calculator

This is the one to use after a run rather than before it. Enter the cumulative distance and elapsed time at each point you recorded, as a watch reports them, and it works out the pace for each individual section as well as the running average up to that point.

Those two columns answer different questions. Section pace tells you what you did on that stretch. Accumulated pace tells you where the race stands overall, which is what matters when you are chasing a target time and need to know whether a slow kilometre has actually cost you.

Running the same route repeatedly and comparing section paces is where this earns its place. It isolates which part of a course you consistently lose time on: a hill, a headwind stretch, or simply the point where concentration goes.

Training by pace and heart rate

Pace is a rate of movement; heart rate is how many times the heart contracts in a minute. They correlate positively, and using both together helps you improve, avoid overtraining, and track fitness over time. Pace tells you what you produced. Heart rate tells you what it cost.

The distinction matters because pace lies in conditions. Heat, hills, wind and fatigue all raise the heart-rate cost of a given pace, so a run that felt hard at an easy pace was probably an easy run your body experienced as hard.

Measuring heart rate and heart rate zones

Heart rate can be measured with a chest strap or wrist monitor, or by counting a pulse at the wrist or neck against a watch. Two figures are used to set training zones.

Resting heart rate for adults is commonly cited as 60 to 100 bpm, though there is an argument that the normal range is really 50 to 90. Lower generally indicates more efficient heart function, but a resting rate below 50 or above 90 can signal an underlying condition.

Maximum heart rate is measured accurately with a cardiac stress test, which raises exercise intensity in stages over ten to twenty minutes. That is inconvenient, so age-based estimates are used instead, most famously:

MHR = 220 − age

It is the most quoted formula and among the least reliable. It was never published with a standard deviation, and maximum heart rates vary widely between people of the same age and training history. Later fits such as 208 − 0.7 × age track the data better, but the individual spread remains large enough that any estimate should be treated as a rough anchor. If your zones feel wrong, they probably are.

Aerobic and anaerobic running

The two come up constantly in endurance training and differ in the duration and intensity of muscular contraction, and in how the muscle generates energy. Anaerobic work sits around 80 to 90% of maximum heart rate in short intense bursts; aerobic work sits around 70 to 80% and can be sustained.

In aerobic exercise there is enough oxygen for the muscles to produce all the energy needed. In anaerobic exercise the cardiovascular system cannot deliver oxygen fast enough, so muscles break down sugar instead, producing lactate as a by-product. Accumulating lactate is associated with the burning sensation and the rapid drop in performance that follows.

This matters most for long events. The aerobic threshold pace is the pace you can hold while drawing energy mainly through aerobic means, balancing fat and carbohydrate use. It is a relatively low intensity and is usually the right pace for the long runs in marathon training, the ones people habitually run too fast.

The anaerobic threshold pace is where glycogen rather than oxygen becomes the primary energy source. Anaerobic training makes you fitter overall, but it is not the foundation of marathon preparation, because that pace cannot be held for long. It has its place; it is not the bulk of the work.

Lab testing is the accurate way to find both thresholds, but they can be estimated. A 2005 study found the most accurate field method for anaerobic threshold is a 30-minute time trial, taking the average heart rate over the final 20 minutes. In practice, threshold pace is close to what you could race for about an hour.

Threshold training means pushing back the point at which lactate starts accumulating, which pushes back fatigue and lets you run further and faster before it arrives.

What the numbers cannot tell you

A pace calculator assumes constant effort on flat ground. Three things break that.

Hills. Climbing costs far more time than descending gives back, so an undulating course is slower than a flat one of the same distance even if the start and finish are level.

Heat. Endurance performance degrades once the temperature rises much above the low teens Celsius, and the effect compounds with humidity. Marathon times fall away sharply in warm conditions.

Race-day distance. GPS watches routinely record a marathon as 42.4 to 42.6 km, because the course is measured along the shortest legal line and nobody runs it. Pacing to your watch's pace reading rather than the mile markers is how runners finish slower than their splits suggested.

Predicting a race time from a shorter one has its own rule of thumb: doubling the distance adds roughly 5 to 6% to the pace. That is why a marathon is much slower than twice a half.

Reading the result

Use the pace mode to understand a run you have done, the time mode to plan one you have not, and the multipoint calculator afterwards to see whether the plan survived contact with the course. Our Calories Burned Calculator and Target Heart Rate Calculator cover the effort side of the same session.