Pace Calculator

How this is calculated

pace (min/km) = total minutes ÷ km   ·   min/mile = min/km × 1.609   ·   km/h = 60 ÷ pace

Worked example (the defaults): 5 km in 25:00 is 5:00 per km — 8:03 per mile, 12 km/h. Held flat, that pace delivers a 50:00 10K, a 1:45:29 half, and a 3:30:58 marathon. The projections assume no fade, which for anything beyond your training distance is optimistic by design — see the FAQ.

Common race-pace anchors

Goal	Pace /km	Pace /mile
Sub-25 5K	5:00	8:03
Sub-50 10K	5:00	8:03
Sub-2:00 half	5:41	9:09
Sub-4:00 marathon	5:41	9:09
Sub-3:00 marathon	4:16	6:52

Pace, speed, and why runners use the inverse

Speed and pace describe the same thing upside down. Speed is distance over time — kilometres per hour, the way a car reads. Pace is time over distance — minutes per kilometre or per mile, the way a runner thinks. Runners prefer the inverse because races are fixed distances, so pace multiplies straight into a finish time: 5:00 per kilometre over 42.195 km is 3:31, arithmetic you can do in your head at 30 km when you have stopped being able to do anything harder.

It also makes improvement legible. Going from 6:00 to 5:30 per kilometre is thirty seconds a kilometre and three and a half minutes over 10 km; expressed as speed, the same change is 10.0 to 10.9 km/h, which conveys much less about what it will feel like on race day.

Even pacing, and the mistake nearly everyone makes

Almost every distance world record has been set on even or slightly negative splits — the second half run at the same pace or marginally faster than the first. Almost every amateur race is run on strongly positive splits, because the first few kilometres feel effortless in a crowd and adrenaline hides the cost. The penalty is not symmetrical: banking two minutes early typically costs four or more later, because starting too fast burns limited glycogen and accumulates fatigue that no amount of later restraint recovers.

A negative-split plan is uncomfortable in the right way. Run the first quarter feeling held back, settle into target pace, and allow yourself to lift only in the final quarter if the effort is there. If you feel strong at 30 km of a marathon, you paced it correctly; if you felt strong at 10 km, you almost certainly did not.

Converting a time at one distance to another

Race times across distances follow a predictable relationship: Peter Riegel's formula, T₂ = T₁ × (D₂/D₁)^1.06, predicts a longer-distance time from a shorter one and is accurate to a few percent for well-trained runners between about 5 km and the marathon. The exponent above 1 encodes the obvious truth that you cannot hold 5 km pace for a marathon.

It comes with a large caveat: it assumes you have trained for the longer distance. A runner with a fast 5 km and a longest run of 15 km will not produce the marathon time the formula predicts, because the limiting factor at that distance is endurance rather than speed. Use it to set a realistic target when your training supports the distance, and ignore it when it does not.

What moves your pace on the day

Heat is the largest environmental factor and it is routinely underestimated: performance begins to degrade above roughly 15°C, and by 25°C most runners lose several percent, which on a marathon is many minutes. Humidity compounds it by blocking evaporative cooling. Hills cost more going up than they return coming down, so a rolling course is slower than a flat one of identical elevation gain and loss. Altitude reduces available oxygen from a few thousand feet upward. Wind costs more into it than it gives back behind.

Plan for conditions rather than fighting them. Adjusting a target pace by ten to twenty seconds per kilometre on a hot day is not a concession; it is the difference between a slower finish and a walk.