# How can I calculate underwater pressure quickly

1. Jul 14, 2015

### Charlie Kay

Does anyone know a simple formula to calculate underwater pressure?

2. Jul 14, 2015

### Staff: Mentor

3. Jul 14, 2015

### Charlie Kay

I have the formula "P=r*g*h" when r=fluid density, g=Acceleration of gravity and h=height of fluid.

Got this off NASA

4. Jul 14, 2015

### Staff: Mentor

Same thing. ($\rho$ is the common symbol for density.)

5. Jul 14, 2015

### Bandersnatch

The simplest way you can get is 1 extra atmospheric pressure per 10 metres of water column.

6. Jul 14, 2015

### Charlie Kay

Brilliant, that's just what I was looking for! :-)

7. Jul 14, 2015

### Charlie Kay

How much Is normal atmospheric pressure?

8. Jul 14, 2015

### Bandersnatch

1 atm or very close to 1 bar, or very close to 100 000 Pascals.

In the spirit of the forum I'd encourage you to take the earlier-posted equations and plug in the numbers for 10 metres of water, and see if it really comes down to 100 000 Pascals. You need density of water in kg/m^3.

9. Jul 14, 2015

### Staff: Mentor

Of course Bandersnatch's answer is an approximation - but quite good enough for all practical purposes. It would be a good exercise to calculate exactly what the pressure increase from ten meters of water is using the $\rho{g}h$ formula - google will find the values of the various physical constants you'll need - and see just how good of an approximation it is, whether it is sensitive to small changes in the temperature of the water.

10. Jul 14, 2015

### Charlie Kay

Thanks:-)

11. Jul 14, 2015

### Charlie Kay

Just wandering if there are any other formulas for it?!

12. Jul 14, 2015

### Staff: Mentor

$\rho{g}h$ is pretty much the gold standard here. You can make additional corrections if $\rho$ or $g$ aren't constant, but for any problem involving reasonable liquids on or around the surface of the earth, these are just rounding errors.

13. Oct 2, 2015

### Charlie Kay

Hey guys I've collected some information and I can now calculate "P=r*g*h" It is:

999.99 X 9.81 X 11000 = 107 908 920.9
Fluid Density X Acceleration Due To Gravity X Height Of Fluid = Pressure

But this is it pascal, does anyone know the conversion rate from pascal to bar???

14. Oct 2, 2015

### Staff: Mentor

1 bar = 100,000 Pa.

15. Oct 2, 2015

### Staff: Mentor

While we appreciate the traffic, Google will answer these questions in milliseconds...

16. Oct 2, 2015

### DaveC426913

And don't forget what 'snatch said: "1 extra atmospheric pressure per 10 metres".
People often forget there's an initial 1 atm at sea level.

17. Oct 2, 2015

### Staff: Mentor

That often falls out of the analysis (for example, for a submarine), but yes, that thought should at least be processed at the start of the analysis.

18. Oct 2, 2015

### Charlie Kay

But it's not as friendly and it doest'n give you a straight answer

19. Oct 2, 2015

### Staff: Mentor

It certainly has its limitations, but it is a life-skill everyone should have.

20. Oct 2, 2015