# CalcRun: Runner Calculators

> CalcRun is a free online toolkit of running calculators for athletes of all levels — from beginners to experienced marathon runners. The site helps calculate pace, time, distance, splits, heart rate zones, lactate threshold, VDOT, and race predictions. All calculators work in both metric (km) and imperial (mi) units and are optimized for mobile and desktop use.

## Calculators

### Core Training & Race Calculators

- [Running Pace Calculator](https://calcrun.net/pace-time/)
  Calculate pace, time, or distance for any run. Enter any two values to find the third. Supports all common race distances (5K, 10K, Half Marathon, Marathon, 100 mi) and custom distances. Formulas: Pace = Time / Distance; Time = Pace × Distance; Distance = Time / Pace. Works in min/km and min/mi.

- [Race Time Predictor](https://calcrun.net/predictor/)
  Predicts your finish time at a new race distance based on a known recent result. Uses Peter Rigel's formula (T₂ = T₁ × (D₂/D₁)^1.06), first published in Runner's World in 1977. Useful for planning from a 5K result to a Half Marathon or Marathon.

- [Split Calculator](https://calcrun.net/split/)
  Generates a pace split table for a target race or workout. Supports even splits, negative splits (−1%, −2%, −3%) and positive splits (+1%, +2%, +3%). Choose any lap length and distance.

- [Lactate Threshold Calculator](https://calcrun.net/lactate-threshold-calculator/)
  Calculates lactate threshold pace and heart rate zone based on user input. Lactate threshold is the intensity at which lactate starts accumulating in the blood faster than it can be cleared — a key metric for distance runners.

- [Heart Rate Training Zone Calculator](https://calcrun.net/heart-rate-zone-calculator/)
  Calculates personalized heart rate training zones (Zone 1–5) based on max heart rate or lactate threshold heart rate. Helps structure aerobic base, tempo, and interval sessions.

- [VDOT Running Calculator](https://calcrun.net/vdot/)
  Calculates VDOT (a proxy for VO2max) from a race performance using Jack Daniels' formula. VDOT can be used to compare performances across distances and to derive training paces. Recommended for race distances between 1500 m and 50 km.

### Conversion Calculators

- [Pace Converter](https://calcrun.net/pace-convert/)
  Instantly converts between min/km and min/mi, and between km/h and mph. Useful for runners switching between metric and imperial systems.

- [Running Distance Converter](https://calcrun.net/distance-converter/)
  Converts running distances between kilometres, miles, yards, and furlongs.

## What Each Calculator Can Answer

- **Pace Calculator**: "What pace do I need to run a sub-4:00 marathon?" / "If I run at 5:30/km, what will my 10K time be?"
- **Race Predictor**: "I ran 10K in 48 min — what can I expect in a half marathon?"
- **Split Calculator**: "Show me splits for a 42.2 km race with a 2% negative split at 5:00/km pace"
- **Lactate Threshold Calculator**: "What is my threshold pace and at what heart rate should I train?"
- **HR Zones Calculator**: "What are my Zone 2 and Zone 4 heart rate ranges?"
- **VDOT Calculator**: "What is my VDOT score from my 5K result?"
- **Pace Converter**: "Convert 4:30 min/km to min/mi"
- **Distance Converter**: "How many miles is a 10K?"

## Blog Posts

- [Lactate Threshold Running: What it is, why it matters, and how to train it](https://calcrun.net/lactate-threshold-running/)
- [Zone 2 training: Complete guide for runners](https://calcrun.net/zone-2-training-guide-for-runners/)
- [What is VO2 max and how to improve it](https://calcrun.net/vo2max-for-runners/)
- [Runner's Knee: Causes, Symptoms and Treatment](https://calcrun.net/runners-knee/)
- [Plantar fasciitis for runners: Causes and recovery tips](https://calcrun.net/plantar-fasciitis-for-runners/)

## Categories

- [Running Blog](https://calcrun.net/blog/)
- [Training](https://calcrun.net/blog/training/)
- [Injuries](https://calcrun.net/blog/injuries/)

## Optional

- [Sitemap index](https://calcrun.net/sitemap_index.xml)
- [About CalcRun](https://calcrun.net/about/)