How do I calculate marathon pace?

Divide your target by 42.195. A four hour marathon is 14400 ÷ 42.195 = 5:41 per kilometre, or 9:09 per mile. Halfway comes at 2:00:00 and 30 km at 2:50:38. Those are averages for an even race, which is what to aim at even though comparatively few marathons are actually run that way.

What is the wall, and why 30 km?

The wall is glycogen depletion — your muscles and liver store roughly enough carbohydrate for around two hours of hard running, which for most marathoners runs out somewhere around thirty kilometres. What follows is not a lack of willpower but a genuine fuel shortage, and it feels like the pace suddenly becoming impossible rather than merely hard. Taking on carbohydrate throughout delays it substantially; nothing eliminates it entirely.

How much does fading in the last 12 km cost?

Your pace multiplied by 12,195 metres multiplied by the fade. For a four hour target holding 5:41 to 30 km, a ten percent slowdown means running the closing stretch at 6:15 and finishing at 4:06:56 — nearly seven minutes lost. Twenty percent costs almost fourteen. That is the arithmetic; the reason to care is that most amateur marathons look much more like the second case than the first.

How much fuel do I need for a marathon?

Common practice is thirty to sixty grams of carbohydrate an hour, so a four hour marathon means roughly 120 to 240 grams in total — about six to eleven gels at twenty-two grams each. The upper end of that range needs training to tolerate, since absorbing that much while running is a trainable skill rather than a given. Practise the exact products and timing on long runs; race day is the worst possible time to find out how your stomach responds.

Should I aim for even splits or plan to slow down?

Aim even, and plan conservatively enough that even is achievable. Every marathon plan targets an even or slightly negative split because that is how the fastest times are run, but the honest position is that most amateur runners finish slower than their halfway split implied. The practical resolution is to set a target you can hold rather than one you can start — going out at a pace you can only sustain for 30 km guarantees the last 12 will be worse than the arithmetic suggests.

Can I double my half marathon time?

No. Riegel's model puts a two hour half at about 4:10:12 rather than a flat four hours — roughly ten minutes more — and even that tends to be optimistic. The model accounts only for the running, while doubling the distance also doubles the fuelling problem and introduces the glycogen limit that a half never reaches. A marathon predicted from a half is a ceiling, not a forecast.

What should my long run build up to?

Around thirty to thirty-five kilometres for most runners, not the full distance. Running the whole marathon in training costs far more in recovery than it adds in fitness, and the adaptations you need come from accumulated weekly volume rather than from any single heroic effort. The long run is also the place to rehearse fuelling, since it is the only session long enough to test whether your plan actually works.

How long is a marathon exactly, and why the odd distance?

42.195 kilometres, or 26.2188 miles. The figure comes from the 1908 London Olympics, where the course ran from Windsor Castle to finish in front of the royal box in the stadium, and it was formally standardised in 1921. After forty-two whole kilometres there are still 195 metres to run; after twenty-six whole miles there are 352. That closing fragment is worth about a minute at most amateur paces.

Does the weather change a marathon time much?

More than at any shorter distance, simply because you are exposed for so long. Heat is the dominant factor — above roughly 15 °C most runners slow measurably, and a warm humid day can add ten minutes or more to a four hour marathon at identical effort. The sensible response is to adjust the target on the morning rather than to hold the original pace and hope, since heat compounds the fade rather than merely adding to it.

Marathon Pace Calculator

Pick a marathon target and this gives you the pace, every split in kilometres or miles, the 30 km checkpoint that actually matters, and — the part no other distance needs — what fading in the closing stretch will cost you. A marathon is 42.195 km, or 26.2188 miles. After forty-two whole kilometres t...

YOUR MARATHON TARGET

TARGET TIME — h:mm:ss

COMMON TARGETS

YOU NEED TO HOLD

5:41 / km

PER MILE

9:09

HALFWAY

2:00:00

AT 30 KM

2:50:38

10.55 km/h over 42.195 km — 26.2188 miles. The 30 km split is the one to watch: everything before it is preparation, and the closing 12.195 km is where the time is actually decided.

SPLITS

1 km

1.0 km