There are a number of methods to predict your potential time at a distance from a distance and time you already know or have achieved. Some require some solid math and patience (especially for the math-challenged). Other approaches use a chart that you just look up your corresponding distances/times. And of course, some are put online and take the mental gymnastics out of it. There are actually quite a few formulas available. But this should give you an introduction to using them.
Here, I’ll demonstrate the calculations for; Horwill’s Law, Running Trax tables, Galloway’s formula, vVO2max time trial test. Then I’ll compare them with real performances (mine).
In each case, the distance/time is assuming an all out race effort. So, when it says your “mile time” it means an all out single mile time trial or raced mile on a track while feeling fresh and with a complete and proper warm up in moderate environmental conditions. A flat and precisely measured road course could subsititute.
Horwill’s Law is simple and straight forward math. Take a distance and time and determine the pace per 400 meters (Ok, a quarter mile will be close enough too.. except for the engineers and accountant types in the readership). Now, every time you double the race distance, add 4 seconds to that 400 meters (elite are 2-3 seconds per 400). You can just as easily add about 16 seconds per mile pace. So, if you can run a mile in 8:00 we could estimate that you can run at a pace of 8:16 per mile for two miles or about 16:32. Or you could run about 8:24/mile for 5K which is 26:02.
J. Gerry Purdy developed a point scale for distances called Running Trax. It is based on years of statistical data analysis. For simplicity, “world bests” sort of anchor the high side and equaling 1000 points. Since tables have not been updated recently, some world records actually are higher than 1000. There is a software that you can obtain with the book. If you can run at 8:00 mile that is awarded 230 points. A similar 230 point effort for two miles would be 16:25 (229 points). Or you could run 26:12 for 5K.
Jeff Galloway uses the following method. It is based on personal data and experience. Take your one mile time and adjust it as follows: add 33 seconds for your pace for a 5K; or multiply it by 1.15 for 10K pace; or multiply by it by 1.2 for half marathon pace; or you can multiply it by 1.3 for marathon pace. So, if you run a 8:00 mile this system estimate that you could run 8:33 per mile for 5K or 26:30. It is limited to those distances but you could interpolate intermediate distances/times.
A scientific method based on research of many elite runners as well as supported in many research studies is to use a percentage of your vVO2max. You can find this pace by doing a 6:00-7:00 time trial. The research varies a bit depending on whether we are measuring elite or completely non-conditioned runners (from 4:00 to as much as 8:30, with most of us falling in between and the most common number used is 6:00). Personally, as a coach I use a 1600 or 2000 meter time trial depending on the caliber of the runner. With this method you divide your per mile pace by the percentage of VO2max attained by well trained individuals to get your projected pace. You divide by .95 for 5k, .90 for 10k, .80 for the marathon. Marathon times vary widely depending on level of ability and conditioning however. If you time trial yielded 8:00 then your projected 5k pace is 8:25/mile or 26:06 for the 5k. It is also limited but you could interpolate intermediate distances/times.
As you can see, these are reasonable projections and each offer similar times. (26:02, 26:06, 26:30, 26:32) You will find variations in calculations as distances move up or down. Some will seem more accurate on distances that are close together (i.e. 5k projected to 10k) and less accurate the larger the gap (i.e. mile to marathon). You will probably find one method or formula that just is easier to use.
There is an important caveat to all this prediction stuff. It assumes that you:
1. Have completed appropriate training for the given projected distance.
2. The course is flat.
3. The weather is moderate (i.e. in 60-70F degree range).
4. The race is appropriately paced (i.e. even paced).
5. You are appropriately rested, feel good or fresh and it is a “good” race.
My experience with using these is that none are perfect. Some are easier to use than others. Some may be more accurate for beginners than more experienced runners. For some individuals one formula may be more accurate than another formula. But, be careful not to advocate one formula “because it is accurate for you”. It may not work as well for someone else. My personal preference is a scientific basis so I use the vVO2max research approach. Ultimately, what is easiest and works for you is what is important. As you can see from the table with my personal examples, they are all reasonably close.
These calculations also reveal what I trained for most of the time – 5k-10k distances. I never trained for the half mile or half marathon. I was only semi-serious about the marathon and have only run four half-marathons ever. I believe I could have run in the 2:28 and 1:10 range for each respectively.
A real mis-use of these calculations is to take them as gospel. The five assumptions I listed are seldom attained. Therefore, it will be rare these are absolutely precise. In any event they can do several very beneficial things.
1. They provide an estimate of your abilities if you train appropriately.
2. They give you a reality check on “goal” times you’ve set for various distances.
3. They provide guidance for “goal paced” runs.
4. They provide a nice comparison of efforts you have already run at various distances.
5. If there is a wide discrepency in your projected and real times, it most likely indicates you need to change your training.
6. They can provide motivation.
Use them in good health!