Running pace calculator

How the math works

Pace is simply time divided by distance. The calculator converts between kilometers and miles (1 mile = 1.609 km) and also shows your speed in km/h and mph.

Race predictions use the formula Pete Riegel published in 1981:

T2 = T1 × (D2 ÷ D1)^1.06

T1 and D1 are your known time and distance; D2 is the race you want to predict. The 1.06 exponent reflects that you slow down a little as races get longer.

Worked example

You ran a 5K in 25:00 (1,500 seconds). Predicted 10K: 1,500 × (10 ÷ 5)^1.06 = 1,500 × 2.085 ≈ 3,127 seconds, or about 52:07.

Using predictions sensibly

• Use a recent, all-out result on a flat course. A training run gives a slower prediction.
• Predict up one step, not three. 5K to 10K is reliable; 5K to marathon is a rough guess.
• Endurance must match. The prediction assumes you've done the training for the longer distance.

New to running? Start with the 8-week walk-run plan, and use setting realistic race goals once you have a race in mind. For effort by heart rate instead of pace, try the heart rate zone calculator.

Pace vs. speed in plain terms

Pace and speed describe the same thing from opposite directions. Speed tells you how far you go in a set time, such as 10 km/h or 6 mph. Pace tells you how long it takes to cover a set distance, such as 6:00 per km or 10:00 per mile.

Runners usually prefer pace because it maps straight onto a race: pace times distance gives your finish time. Treadmills often display speed, which is why the calculator shows both.

One thing that trips people up: with pace, a lower number means you are running faster. A 5:30 pace is quicker than a 6:00 pace.

Reading and converting min/km and min/mile

A pace of 5:30 means 5 minutes 30 seconds per kilometer or mile. Because a mile is about 1.609 km, the same effort always shows a bigger number per mile:

• 5:00 per km is about 8:03 per mile (12 km/h).
• 6:00 per km is about 9:39 per mile (10 km/h).
• 10:00 per mile is about 6:13 per km (6 mph).

To convert by hand, turn the pace into seconds, multiply or divide by 1.609, then turn it back into minutes and seconds. For 6:00 per km: 360 seconds × 1.609 ≈ 579 seconds, which is 9:39 per mile.

Choosing training paces by feel

Most of your running does not need a target number. Effort matters more than the watch, especially when you are tired, it is hot, or the route is hilly. The simplest tool is the talk test:

• Easy: you can speak in full sentences without gasping. This should be most of your weekly running. If you are unsure, go slower.
• Steady: you can still talk, but in shorter phrases. It feels purposeful but sustainable.
• Tempo: "comfortably hard." You can say a few words at a time, but you would not want to hold a conversation. For many runners this is close to the pace they could hold for about an hour in a race.

Use pace as a rough check afterwards, not a target you force on every run. Heart rate can be another useful guide; see heart rate zones explained for how the zones line up with these efforts.

Setting a realistic race goal and pacing it evenly

A good goal is based on what you have actually run recently. Here is a simple way to set one:

1. Take a recent, honest race or time trial over a shorter distance.
2. Run it through the predictor above to get a ballpark finish time.
3. Adjust for the course, the weather and how consistent your training has been. If in doubt, start with a slightly slower goal.
4. Divide the goal time by the race distance to get your target pace.

The most common race mistake is starting too fast. Adrenaline and fresh legs make goal pace feel easy early on, so it is tempting to "bank time," but that time is usually paid back with interest later. Run the first part at or slightly slower than goal pace, settle in through the middle, and pick it up only if you feel strong near the end.

A gradual warm-up makes the opening pace feel smoother; see how to warm up before exercise for a simple routine.

Why predictions get less reliable for longer races

The Riegel formula assumes you slow down by a steady, predictable amount as the distance grows. That holds up reasonably well from 5K to 10K, or 10K to half marathon. Beyond about 90 minutes of running, other factors take over:

• Stored carbohydrate runs low, so fueling starts to matter.
• Muscle fatigue and general endurance count for more than raw speed.

So a 5K-based marathon prediction is often too optimistic, especially with lower weekly mileage. Treat it as a best case and build in margin.

Heat, hills, wind and other conditions

The same effort can produce quite different paces depending on the day. In general:

• Heat and humidity make the same pace feel harder. Slow down, drink to thirst, and be ready to adjust your goal on a warm race day.
• Hills slow you on the way up, and the time you gain coming down rarely makes up for it fully. Aim for even effort on climbs rather than even pace.
• Wind costs more running into it than it gives back behind you.
• Trails, snow and altitude also tend to slow your pace at the same effort.

Treadmill vs. outdoor pace

Treadmill pace and outdoor pace are not always equal. On a treadmill there is no air resistance and the belt helps move your feet, so the same displayed pace can feel a little easier than outdoors. Many runners set a small incline, around 1%, to make it feel closer to running on flat ground outside.

Treadmill displays are not always precisely calibrated, either. If the numbers seem far apart, trust the talk test over the screen.

How beginners should think about pace

If you are just starting out, pace is the least important number to worry about. Focus on time on your feet first: building up to 20 or 30 minutes of continuous easy running (walk breaks are fine) a few times a week. Speed tends to come with consistency.

Build up gradually, keep most runs easy, and take rest days. For recovery, see sleep and recovery for training. For a sense of how much weekly activity to aim for overall, read how much exercise you need per week. If you want to estimate the energy you use on your runs, the calorie calculator can help.

When to stop and see a doctor

Pace targets should never override warning signs from your body. Stop running and seek medical help if you have chest pain or pressure, severe shortness of breath, dizziness or fainting, or an irregular or racing heartbeat that does not settle. See a doctor or physical therapist about pain that gets worse as you run, makes you limp, or lingers for more than a few days. If you have a heart condition, other health concerns, or have been inactive for a long time, check with your doctor before starting a new running plan or racing hard.

The numbers from this calculator are estimates to help you plan. How you feel on the day is always the better guide.

Based on: Riegel race prediction formula (1981).