Most writers refer to speedwork repetitions in meters because they’re often run on a competition track, and such tracks can measure out 100 meter increments. On a track, you can run exactly 200, 300, 400, 1200, 2800, etc, meters.
Of course, many don’t have access to a track, and many American runners don’t use the metric system given our nation refers to distance in imperial miles.
The easy answer for conversions is that 400 meters is about 1/4 mile, 1600 meters is about a full mile, and so on.
But another complication of not running on a track is that measuring out exactly a quarter mile for a rep, let alone 400 meters, on a public right of way is unclear and difficult. Our parks paths, landmarks, etc, aren’t ever spaced out exactly right. A space between two light posts, benches, ends of a stretch of path, city block, can be 530 meters, 0.3 mile, 677 meters, etc.
Plus, relying on your GPS watch for distance doesn’t solve the problem, because your GPS readings aren’t totally accurate. A mapped run often shows you running through landmarks as the GPS signal guesstimates your actual route. It certainly won’t measure out your exact distance or velocity. Map the actual route run on an Open Maps interface, and you’ll find a difference of several tenths of a mile.
So how do you run those 800 meter repeats, or quarter mile repeats?
The answer is to not worry about differences in distance. Find a stretch of useful pathway with a distance that’s close enough, and just run that.
For example, there’s a pedestrian bridge near my home. If I ran from the bottom of one ramp, across and down the other ramp, that would total about 350 meters.
If I wanted to run 400 meter repeats at a 5K pace, I’m not exactly ruining anything if I just ran the repeats on that bridge and adjusted my time expectations for the difference… especially given that the sharp turns and elevation grade of the ramps would effectively make up for any lost difficulty from a shorter rep.
Let’s say there’s a usable 4.7 mile loop trail near my home. If I wanted to do a 5 mile tempo run, I’m not losing anything doing the run on that trail and calling it good. The lost 0.3 miles isn’t a substantial difference, any more than doing the run on the trail’s soft surface.
In both cases, eliminating the stress of worrying about the correct distance can augment the quality of the workout. Just get your tempo run or speed reps in on your improvised course and calling it good can allow you to focus more on your work in the rep of the run.
The goal of these workouts after all isn’t running the exact distance. With speed reps, it’s about working on your running form economy and efficiency, moving your body as quickly as possible with correct, repeatable form. With tempo work, it’s about making your body maintain a heightened, somewhat anaerobic running state for a general period of time.
Remember that every workout has a specific biomechanical goal for your body. It’s not an accounting exercise in running the exact, correct mileage. Sure, you don’t want to run 12 or 30 miles when the plan was to run 20 miles. You don’t want to do 3 reps of 200 meters when the plan was to run 8 repeats of 400 meters.
You want to get close to the specified goal of the workout, and that might require you add reps, or maybe double back and run the same course again to finish a tempo run.
For example, if my original workout plan to run 10 reps of 400 meters but I only have access to that 350m bridge path, maybe I run 11 reps instead of 10 to make sure I get the needed volume of speedwork.
The point is that there’s no need to get the length of the path exactly right, when it’s not possible. Once you find a “course” that’s “close enough”, that’s 90% of the battle.
Obviously, as always, conditions like weather and terrain are concerns, plus getting to and from the workout. You need to account for those like you would any other workout.
But don’t sweat finding the exact course you need if one isn’t available. Look at a map, find a suitable course that gives you close to the needed distance, and just run that.