How Do My Lap Times Convert to Open Water Times?

If you’re signed up for an open water event this summer, you’re probably wondering how all the pool training you did over the winter will translate to open water. And, in particular, whether you can estimate your anticipated finish time based on your pool times.

In fact for some open water events, you’ll be asked to estimate your anticipated finish time so you’re placed in the appropriate start wave. If you’re new to open water swimming or haven’t completed a swim of that length before, you might be wondering how you can figure this out.

The good news is, with a little calculating and some educated estimating, you can figure out how your lap times will convert to open water times.

The basic formula is to take your average pace per 100 yards or meters and extrapolate from there. This method usually works best for longer pool distances—200 yards or more. That’s because the more 100s you swim in succession, the more you’ll settle into your pace, giving you a more accurate average time per 100.

For example, if you swim a 500 in practice in a time of 8:00, your pace per 100 is 1:36. In open water you don’t have the benefit of pushing off walls, so your pace per 100 is going to be slower by roughly 5 seconds or more. Add in wind and waves, and you could be slower still.

A good basic approach is to add 10 seconds per 100 to estimate your open water pace. So, in the example above, if you’re the swimmer taking 8:00 to swim a 500, you’re looking at an open water pace of about 1:46 per 100.

With that info in hand, you can then calculate how long it might take you to swim a mile, a kilometer, or multiples thereof. A swimmer who’s holding 1:36 per 100 yards in the pool would be looking at a mile time of about 30:00. If you’re holding 1:36 per 100 meters in the pool, your kilometer time would be 18:00.

Again, water and weather conditions on race day can alter your pace significantly, so remember these are just ballpark estimates to give you a sense of what to expect when swimming in open water.

As with any swimming event, the better you train, the better you’ll perform on race day. It’s a good idea to test yourself throughout the course of your training season with a few time trials to make sure you’re staying on pace and making progress toward your goals.

A timed pool 1000 or 2000 or longer swim, such as any of the Virtual Championship swim events offered by USMS, can provide a lot of insight about your stamina and ability to hold a steady pace, while also preparing you for the rigors of open water.