Today’s question comes from Done van Eck. Done wanted to know what formula you use to work out your race pace for example if you take your 5km run time and multiply it by 2.1 you should get your 10km time. How can you take your 5km run time and convert that to your half marathon, 32km or your marathon time?

Brad Brown: Today’s question comes from Done van Eck. Done wanted to know what formula you use to work out your race pace for example if you take your 5km run time and multiply it by 2.1 you should get your 10km time. How can you take your 5km run time and convert that to your half marathon, 32km or your marathon time?

Lindsey Parry: To be honest I would probably have to sit down and do some maths for you. This sounds ridiculous but I just know instinctively when someone gives me a 5km run time what they should be capable of for a 10km or a half marathon.

I guess from a conversion from a 5km to a 10km, I look at the slowing down at about 3%. So if we work out your average pace and we multiply that by 3% that would give you a reasonable idea for a 10km.

When we convert that from a 10km to a 21km you’re looking at maybe another 3% or possibly 4%, somewhere around there. From a half marathon to a marathon again you’re looking at between 3% and 5% you’ll slow down and be able to hold that for a marathon.

5km run time calculations

It’s probably one of the better questions I’ve been asked. I often get asked “if my 5km run time is this, what can I run for a 10km?” and I just instinctively know the answer and I’m normally only a handful of seconds out.

Maybe we should revisit this one in a week or two from now. When I look at all these times and I write them all down I will start getting an idea for the formula my brain is using.