---
title: "About Run Pebble: Free Running Calculators | Run Pebble"
description: "What Run Pebble is: free running pace, prediction, split, treadmill, fuel and log tools that work in your browser, and where their numbers come from."
url: https://runpebble.me/about/
---

About

# About Run Pebble

Small, free calculators for recreational runners, from a first 5K to a marathon.

## What it is

Run Pebble works out pace, time and distance, predicts race times from a recent race, plans even or negative splits with a printable pace band, converts treadmill speeds, plans carbohydrate and fluids for a race, and keeps a simple running log. Kilometres and miles sit side by side everywhere.

## Where the numbers come from

Each page lists its sources in a short “Sources” section: World Athletics for race distances, NIST for the mile, Riegel’s 1981 paper for race prediction, Jones and Doust (1996) for the 1% treadmill incline, the joint ACSM, Academy of Nutrition and Dietetics and Dietitians of Canada position stand and the ACSM fluid position stand for fuelling, and a randomised trial for the “10% rule”. Where the evidence has limits, the page says so. Everything here is general guidance, not medical advice.

## How it works

The calculators run entirely in your browser. Nothing you type is sent anywhere, there are no accounts, ads or cookies, and the pages keep working offline once loaded. The running log is saved only in your browser’s local storage. The site uses Cloudflare Web Analytics, which counts page views without cookies or cross-site tracking and never receives what you type into the tools. The [privacy page](https://runpebble.me/privacy/) has the details.

Spotted a figure that looks wrong? Check it against the source linked on that page, which always wins.