Open Water Sighting Adjustment Calculator
Estimate the extra distance and time an open-water swim really costs once you add course drift and the seconds lost lifting your head to sight.
How it works
Real distance = course ÷ cos(drift angle) · Total time = (real distance ÷ 100)×pace + sights × loss per sight
Without lane lines you rarely swim a perfect straight line: veering off by an angle and correcting back lengthens the path by roughly 1 ÷ cos of that angle. On top of the extra swimming, every time you lift your head to sight the buoy you break your streamline and lose a fraction of a second. Together these explain why an open-water 1,500 m almost always takes longer than the same distance in a pool.
Worked example
On a 1,500 m course with an 8° average drift, the real path is 1,500 ÷ cos 8° ≈ 1,515 m — 15 m extra. At a 1:40 per-100 pace that path takes about 25:15, and 60 sights costing 0.8 s each add roughly 48 s more, for around 26:03 versus 25:00 in the pool.
Frequently asked questions
How much does poor sighting cost?
Drift is the bigger cost for most swimmers: veering 8–10° off line and back adds 1–2% distance, and a wandering swimmer can easily add 5% or more over a long course. Frequent, quick sights keep the angle small — the extra seconds per sight are cheaper than swimming a longer path.
How often should I sight?
In calm water every 6–10 strokes is typical; in chop or a crowded swim, sight more often to avoid large drift. Aim for a low, quick "crocodile eyes" sight so each one costs a fraction of a second rather than stalling your stroke.
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This calculator is for educational purposes. Double-check important results before acting on them.