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5K Pace Calculator

Enter your goal time or current pace to get split targets, finish time estimates, and race predictions — all computed in your browser, nothing sent anywhere.

By Karina Zulmery Suárez Bustos , Industrial engineer
Last updated:

What this Five K Pace Calculator does

This English-language 5K pace calculator takes your goal finish time or a known pace and works out everything you need to run a confident race: pace per kilometer, pace per mile, projected finish time, and Riegel-formula predictions that extrapolate from a recent race effort. Whether you're chasing a sub-25 or your first 5K finish, knowing your exact per-km splits before race day removes the guesswork that causes most runners to go out too fast. The tool runs 100% client-side — your data never leaves your browser. No uploads, no tracking, no server logs. As a bonus, if you're combining run training with nutrition targets, our [Calories Burned Calculator](/en/calories-burned-calculator/) can estimate the energy cost of your weekly mileage.

Features

  • Pace per km and per mile. Outputs both metric and imperial pace simultaneously so you can train with a GPS watch set to either unit without manual conversion.
  • Finish time projection. Enter a known pace and distance run in training to project your expected 5K finish time under similar conditions.
  • Riegel race predictions. Uses the Riegel endurance formula (T2 = T1 × (D2/D1)^1.06) to extrapolate a 5K prediction from any recent race result — a 10K, half marathon, or even a timed mile effort.
  • Even-split breakdown. Displays per-kilometer and per-mile splits for an even-pace strategy, making it easy to program interval targets on a track or treadmill.
  • No install, no account. Runs entirely in the browser. There's no signup, no data stored on any server, and no third-party scripts phoning home with your times.

How to use the Five K Pace Calculator

Three inputs are enough to get a full pace breakdown. All calculations happen instantly in the browser.

  1. Choose your input mode. Select whether you're starting from a goal finish time (e.g. 24:30) or a known pace (e.g. 4:54/km).
  2. Enter your value. Type your target time in mm:ss or hh:mm:ss format, or your per-km / per-mile pace. The calculator accepts both.
  3. Review your splits. The results panel shows pace per km, pace per mile, and your projected finish time. For Riegel predictions, enter a recent race distance and time in the second section.
  4. Copy or share. Hit Copy to grab the result as plain text. Paste it into a training log, a message to your coach, or a note on your phone.

Common use cases

  • Race day pacing strategy. A runner in Dublin training for a local parkrun uses the calculator to set conservative first-kilometer targets, avoiding the classic blow-up from starting too fast in a crowd.
  • Treadmill interval programming. Convert a goal race pace to a treadmill speed in mph or km/h so you can dial in the exact belt speed during a tempo session without doing mental arithmetic mid-run.
  • Extrapolating fitness from a recent race. If you just ran a 10K personal best, the Riegel section predicts what that effort implies for your 5K — useful when you haven't raced the shorter distance in months.
  • Training plan pace zones. Coaches use the finish-time projection alongside tools like the [TDEE calculator](/en/tdee-calculator/) to align a runner's energy intake with their weekly load as race day approaches.
  • Tracking progress over a training block. Logging pace calculations week over week lets you see whether your target pace has improved relative to your perceived effort — a simple proxy for fitness gains.

Frequently asked questions

How is the Riegel prediction calculated?

The Riegel endurance formula is T2 = T1 × (D2 / D1)^1.06. The exponent (1.06) models the non-linear fatigue cost of longer distances. It's a well-tested empirical model, though individual variation in aerobic efficiency means predictions can be off by 1–3% for any given runner.

Does this calculator store my times anywhere?

No. Every calculation runs locally in JavaScript inside your browser tab. Nothing is sent to a server, stored in a database, or shared with third parties. Closing the tab clears everything. This is the same privacy model used by offline-capable progressive web apps.

What's the difference between pace per km and pace per mile?

Pace per kilometer is the time to cover 1 km (e.g. 5:00/km). Pace per mile covers 1.609 km (e.g. 8:03/mi). Most European GPS watches default to km; U.S. runners often use miles. This tool shows both so you don't need a separate converter.

Why does my Riegel prediction seem faster than I expect?

The formula assumes consistent aerobic fitness across distances. If your recent reference race was shorter (like a mile), the model may overestimate your 5K fitness because shorter efforts rely more on anaerobic capacity. Use a 10K or half-marathon reference for more reliable 5K projections.

Can I use this for race distances other than 5K?

The pace and finish-time sections work for any distance — just interpret the splits accordingly. The Riegel section lets you input any reference race distance, so it generalizes well to 8K, 4-mile, or other non-standard distances.

Is there a risk of integer overflow with very large time values?

Not in a pace calculator, but it's a valid instinct — the Year 2038 problem, for instance, is a real concern for systems using signed 32-bit Unix timestamps in infrastructure software. This tool uses JavaScript's 64-bit floating-point numbers for all arithmetic, so time values up to many thousands of hours are handled without overflow.