Pressure to Depth in Water Calculator
Estimate water pressure by depth using the bar-per-10-metres rule. Useful for diving, plumbing, aquariums and any scenario involving submerged equipment.
Last updated: May 2026
Water pressure and depth: the practical relationship
The rule of thumb is 1 bar of pressure for every 10 metres of seawater depth, plus 1 bar of atmospheric pressure at the surface. At 10 m depth: 2 bar total. At 30 m: 4 bar. Fresh water is slightly less dense than seawater (~2.5% lower), so the same depth produces marginally less pressure; 10 m of fresh water generates about 1.97 bar rather than exactly 2 bar.
This matters practically for dive computer settings (most default to seawater), waterproofing ratings on electronics (a 50 m rating does not mean safe for 50 m diving, static vs dynamic pressure), and hydraulic engineering where head pressure drives flow calculations.
Depth and pressure reference (seawater)
| Depth (m) | Pressure (bar) | Pressure (psi) | Context |
|---|---|---|---|
| 0 (surface) | 1.0 | 14.7 | Atmospheric pressure only |
| 10 m | 2.0 | 29.0 | Max recreational snorkeling |
| 18 m | 2.8 | 40.7 | PADI Open Water limit |
| 30 m | 4.0 | 58.1 | Recreational scuba limit |
| 40 m | 5.0 | 72.5 | Advanced recreational limit |
| 100 m | 11.0 | 159.5 | Technical and commercial diving |
Frequently Asked Questions
What is the pressure at 10 metres in seawater?
Approximately 2 bar: 1 bar atmospheric at the surface plus 1 bar from the 10 m water column. In fresh water the same depth gives about 1.97 bar (fresh water is ~2.5% less dense than seawater). For diver planning, seawater figures are used by default.
How does depth affect air consumption for divers?
Pressure directly affects the volume of air breathed per breath. At 10 m (2 bar absolute), a diver breathes twice as much air per breath as at the surface. At 30 m (4 bar), four times as much. A tank that lasts 60 minutes at the surface lasts about 15 minutes at 30 m, which is why dive planning requires accurate depth and time estimates.
Can I use this for fresh water instead of seawater?
The calculator uses the seawater approximation (1 bar per 10 m). For fresh water, multiply the result by 0.975 to correct for lower density. The difference is small for shallow depths but adds up, and at 100 m, seawater gives 11 bar while fresh water gives 10.75 bar.