Race Shape

Race Shape › Calculators

Free tools

Running, cycling and swimming calculators

Free calculators built on the same engine as every Race Shape plan: pace and splits, race-time prediction, training paces corrected for altitude, heart rate and power zones, Critical Swim Speed — and predictors for the 100th Comrades, Two Oceans and the Cape Town Cycle Tour.

The big South African races

Comrades predictor: your time and medalPredict your 100th Comrades time and medal from a marathon: Bill Rowan, Robert Mtshali, Bronze or Vic Clapham, with the pace each medal needs over 90 km.Two Oceans predictor: your 56 km time and medalPredict your Two Oceans Ultra time and medal from a marathon: Silver, Sainsbury, Bronze or Blue, with the pace each needs over 56 km.Cape Town Cycle Tour time predictorA rough Cape Town Cycle Tour or 947 Ride Joburg finish time from your FTP and weight, and how much faster a higher FTP would make you.Marathon pace chartMarathon pace chart with even splits every 5 km for sub-3, 3:30, sub-4, 4:30 and sub-5 — for the Cape Town Marathon, Soweto and every Major.

Running

Running pace calculatorWork out your running pace per kilometre from a finish time, or your finish time from a pace, with even-pace splits for 5 km to Comrades.Race time predictorPredict your 10 km, half marathon, marathon, Two Oceans and Comrades times from one recent race, using Jack Daniels’ VDOT model.Training pace calculatorYour easy, marathon, threshold, interval and repetition paces from one recent race, corrected for altitude in Johannesburg, Pretoria and beyond.Altitude pace calculatorConvert a running pace between sea level and altitude: how much slower the same effort is in Johannesburg, Pretoria or Bloemfontein, and quicker at the coast.Heart rate zone calculatorFive heart rate training zones for running and cycling, from your threshold heart rate, maximum heart rate or just your age.Age grade calculatorYour age-graded percentage for parkrun, 10 km, half marathon or marathon, from the 2025 road tables, with the time each grade takes at your age.VO₂max calculator from a race timeEstimate your running VO₂max (VDOT) from a parkrun, 10 km, half or marathon, and see what each extra point is worth in race time.

Cycling and swimming

Cycling power zone calculatorSeven Coggan power zones from your FTP or a 20-minute, 8-minute or ramp test, with watts per kilo. Sweet spot, threshold and VO₂max in watts.CSS swim calculatorCritical Swim Speed from a 400 m and 200 m time trial, with pace per 100 m for every swim zone and an open-water mile estimate for Midmar.

Quick answers

Every Comrades medal, and what it takes

Wally Hayward · Isavel Roche-Kelly · Silver · Bill Rowan · Robert Mtshali · Bronze · Vic Clapham

Every Two Oceans medal, and what it takes

Silver · Sainsbury · Bronze · Blue

Goal paces

Sub-30 5k · Sub-25 5k · Sub-22 5k · Sub-20 5k · Sub-18 5k · Sub-1 hour 10k · Sub-50 10k · Sub-45 10k · Sub-40 10k · Sub-2:30 half marathon · Sub-2:15 half marathon · Sub-2 hour half marathon · Sub-1:45 half marathon · Sub-1:30 half marathon · Sub-5 hour marathon · Sub-4:30 marathon · Sub-4 hour marathon · Sub-3:30 marathon · Sub-3:15 marathon · Sub-3 hour marathon

Race converters

5 km to half marathon · 5 km to marathon · 10 km to half marathon · 10 km to marathon · half marathon to marathon

South African race predictors

Soweto Marathon · Two Oceans 21 km · Cape Town Marathon · Om Die Dam 50 km · Midmar Mile · Ironman 70.3 Durban · Ironman South Africa

Heart rate charts

By age

Why these numbers can be trusted

Every calculator here runs on Race Shape’s engine: Jack Daniels’ VDOT model for running paces and predictions, Andrew Coggan’s power zones for cycling, Joe Friel’s heart rate zones, and the two-trial Critical Swim Speed protocol for swimming. Paces are corrected for altitude — about 2% for every 300 m above 500 m — and corrected once, for the difference between where you train and where you race.

Where a model stops being reliable, the calculator says so instead of pretending. Past the marathon, predictions follow how real Two Oceans and Comrades fields finish rather than a formula that flatters, and cycling times are labelled as the rough shape of a day decided by bunches and wind.

From a number to a plan

A calculator gives you one number. A Race Shape plan takes your numbers — a time trial, your FTP, your swim test, the days you have and the altitude you train at — and lays out every session to race day, with a lighter week every fourth and a taper timed to your race. Building it is free, and you see the whole block before you pay.

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When to start training for your 2027 race →