How fast can you swim compared with a fish?
Water is 800 times denser than air, which is why the fastest human swimmer is slower than a brisk walk.
1.23 × a lap swimmer
4 km/h is faster than 2 of the 9 references on this page.
Reference figures are measurements and are rounded; the unit conversion behind them is exact.
| Reference | Size | Yours ÷ theirs | Note |
|---|---|---|---|
| casual swimmer | 1.98 km/h | 2.02× | 2 km/h |
| lap swimmer | 3.24 km/h | 1.23× | |
| Olympic 100 m freestyle | 8.24 km/h | 0.485× | World record pace |
| sea turtle | 10.1 km/h | 0.397× | |
| penguin | 11.2 km/h | 0.358× | |
| great white shark | 24.8 km/h | 0.161× | |
| dolphin | 29.9 km/h | 0.134× | |
| nuclear submarine | 46.4 km/h | 1/11.6 | About 25 knots submerged |
| sailfish | 108 km/h | 1/27 | Widely quoted, poorly measured |
Worth knowing
- The 100 m freestyle world record is an average of 2.29 m/s — slower than a brisk walk on land.
- Drag in water rises with the square of speed and the density is 800 times air’s, which caps swimming speed far below running speed.
Frequently asked
How fast can a human swim?
The men’s 100 m freestyle record averages about 8.2 km/h including the dive and turn. Sustained open-water pace for a strong swimmer is nearer 4 km/h.
Can you outswim a shark?
No. A great white cruises at 3 km/h and can burst to 25. The reassuring part is that it is almost never interested.