Pace & Speed Calculator

Metric	Value	Copy
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Checkpoint	Cumulative Time	Copy
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No splits yet. Add distance, time, and split size to see pacing checkpoints.

Running pace and speed are everyday measures of how fast a distance is covered and how long a finish will take. They help you plan sessions, compare races, and set targets with confidence.

You provide a race distance and a finish time, then see pace per kilometre or per mile alongside overall speed. You can also set a target pace or speed so the time updates, and add a split size to preview checkpoints that keep your effort consistent.

A typical use is picking a distance preset, entering a recent result, and checking the matching pace to guide your next workout. Another is setting a goal pace and letting the time adjust so you can see if it fits your schedule and route.

Results assume steady effort and even terrain, so hills, turns, traffic, and stops can change what you feel on the day. Reuse the same units each time and keep inputs consistent so week to week comparisons stay meaningful.

If splits matter for your plan, choose a size that you can hit reliably on the track or the road. When the plan is saved, note the pace and two or three checkpoints you want to memorize for race day.

Technical Details:

The quantities are distance, elapsed time, average pace, and average speed. Pace reports time per unit distance, while speed reports distance per hour. The calculator presents both kilometre and mile systems for comparability.

Speed is computed from distance divided by elapsed hours. Pace is computed from elapsed seconds divided by distance. Conversion between kilometre and mile pacing uses a fixed kilometre per mile factor so values remain consistent across systems.

Interpretation is straightforward. Lower pace values mean faster per‑unit splits, and higher speed values mean more distance covered in an hour. Values near a goal boundary suggest adjusting either distance or time slightly so training steps feel achievable.

\begin{array}{l} v = \frac{D}{T / 3600} & speed (km/h if D in km) \\ p_{km} = \frac{T}{D} & pace (s/km) \\ p_{mi} = p_{km} \times f & pace (s/mi), f=1.609344 km/mi \\ v_{mph} = \frac{v}{f} & speed (mph) \end{array}

Symbols and units used in calculations
Symbol	Meaning	Unit/Datatype	Source
D	Distance	km or mile	Input
T	Elapsed time	s	Input
v	Average speed	km/h or mph	Derived
p_km	Pace per kilometre	s/km	Derived
p_mi	Pace per mile	s/mi	Derived
f	Kilometres per mile	1.609344	Constant

Worked example

\begin{array}{l} D = 10 km \\ T = 0 h + 50 min + 0 s = 3000 s \\ p_{km} = \frac{3000}{10} = 300 s/km = 05 : 00 \\ v = \frac{10}{3000 / 3600} = 12 km/h \\ p_{mi} = 300 \times 1.609344 \approx 483 s/mi = 08 : 03 \\ v_{mph} = \frac{12}{1.609344} \approx 7.46 mph \end{array}

At 10 km in 50:00 you average 5:00 per km and 12.00 km/h, which is about 8:03 per mile and 7.46 mph.

To compute a finish from a target pace, convert the target pace to seconds per kilometre.
Multiply by total kilometres to obtain total seconds.
Round to the nearest second and decompose into hours, minutes, seconds.
To compute splits, choose a split size and convert it to kilometres.
Accumulate checkpoints by adding the split size until the finish, then append the finish time.

Validation limits enforced by the UI
Field	Type	Min	Max	Step/Pattern	Notes
Distance	number	0	—	step 0.01	Unit km or mile.
Time hours	number	0	—	—	Non‑negative integer.
Time minutes	number	0	59	—	Clamped to 0 to 59.
Time seconds	number	0	59	—	Clamped to 0 to 59.
Target pace minute	number	0	59	—	Per selected distance unit.
Target pace second	number	0	59	—	Rounded to nearest second.
Target speed	number	0	—	step 0.01	Unit km/h or mph.
Split size	number	0.01	—	step 0.01	Unit match, km, mile, or metre.

I/O formats and rounding
Input	Accepted Families	Output	Encoding/Precision	Rounding
Distance, time, pace, speed, split size	Numbers with a period decimal	Readable metrics, splits table, JSON	Strings, two or three decimals where shown	Speed to two decimals, seconds to nearest second

Units, precision, and display: distance displays with two decimals when at least ten units and three decimals otherwise. Metre splits display with zero, one, or two decimals depending on size. Speeds display to two decimals. Times round to the nearest second.

Networking and storage: processing is browser‑based. CSV, document, and JSON downloads are created locally. No data is transmitted or stored server‑side.

Assumptions & limitations

Average pace assumes even effort across the full distance.
Splits are spaced at constant distance, not by effort or terrain.
Minutes and seconds fields clamp to 0 to 59 automatically.
A maximum of 500 split rows is produced to avoid excessive output.
Setting split size to zero lists only the finish checkpoint.
Conversion uses 1.609344 km per mile for all calculations.
Switching unit systems converts values and rounds to shown precision.
Displayed decimals trim trailing zeros for compactness.

Edge cases & error sources

Very long durations can overflow practical training guidance.
Floating‑point rounding can slightly shift split times when accumulated.
Rounding to the nearest second can roll 59.5 seconds to the next minute.
Exact last split uses an equality check with a small tolerance.
Non‑numeric input is treated as zero before calculations.
Negative inputs are corrected to zero by validation logic.
Locale commas are not accepted as decimal separators.
Unit switches adjust pace, speed, and distance simultaneously.
Metre splits show fewer decimals for large values.
JSON output types are numeric for values that parse successfully.

Step‑by‑Step Guide:

Running pace and speed planning with splits from your chosen inputs.

Select a distance preset or enter a custom distance.
Enter time in hours, minutes, and seconds.
Optionally set a target pace or speed and apply.
Choose a split size to preview checkpoints.
Copy or download the metrics, splits, or JSON summary for your notes.

Example: 10 km in 50:00 yields 5:00 per km and 12.00 km/h. With 1 km splits you will see nine checkpoints and the finish.

You now have a pace target and checkpoints ready for your session.

FAQ:

Is my data stored?

No. Calculations and file creation run on your device, and nothing is sent to a server.

Files are generated locally.

How accurate are results?

Pace and speed match the defined formulas with rounding to the nearest second and two decimals where shown. Real‑world conditions can change actual outcomes.

Which units are supported?

Distance supports kilometres and miles. Speed supports km/h and mph. Pace reports per kilometre and per mile with a fixed conversion factor.

Can I plan 400 m or 800 m splits?

Yes. Set the split size to a metre value and checkpoints will appear at those intervals until the finish.

What if splits do not land exactly on the finish?

Checkpoints list whole intervals first. The finish is always included and may not align with the last split if the distance is not a multiple of the split size.

Does it work without a connection?

Yes. Once loaded, calculations and downloads continue to work without a network connection.

Troubleshooting:

No results shown. Ensure distance and total time are both greater than zero.
Minutes or seconds jump. Values outside 0 to 59 are clamped.
Unexpected mph or per mile values. Check the selected unit system.
Too many rows. Increase split size to reduce the number of checkpoints.
Decimals look odd. Rounding trims trailing zeros by design.
Copy fails. Your device clipboard may require permission.

If nothing updates after inputs change, reload the page to reset cached state.

Glossary:

Pace: Time needed to cover one unit of distance.
Speed: Distance covered per hour on average.
Split: Checkpoint at a fixed distance interval.
Kilometre: Unit of length equal to 1000 metres.
Mile: Unit of length equal to about 1.609344 km.
Conversion factor: Constant used to map between unit systems.