Calculating how many gallons my pool is.

[WiseguyFish]

I've got a larger in ground vynil lined pool. I just changed the liner, and had it converted to SWCG. My question is how many gallons it holds. It's 40'x18', 8' deep at the deep end, 3' deep at the shallow, it has an accent curve at the shallow end bowing out another 30", and a contured stairwell outside the standard square in the shallow end extending another 4'.

I've heard my local pool folks estimate it at 27,000 gallons. Does that sound right? Any folks out there who can accurately tell me what it is if not?

Thanks in advance, and boy am I glad I found this forum!

--Rick

 

[crookm11]

Welcome to TFP!

Do you have any pictures of the pool? Someone may have the same pool and know how much water it holds.

 

[RobbieH]

Did you try entering your dimensions on the calc at the bottom of the pool calculator?
http://www.poolcalculator.com/

Just get pretty close. Then next time you do chemicals, see how it affects the chemistry. Keep adjusting gallons on the pool calculator and pretty soon you'll have the right volume for the chems you added. Does that make sense?

 

[JasonLion]

Welcome to TFP!

My guess would be around 22,000 to 25,000 gallons. That is assuming that your pool wall goes down about 3 feet vertically and then slope down from there in the deep end, as most vinyl liner pools do. If you describe the shape more throughly, like how rounded the corners are and how much slope there is in the deep end, we can give you a better estimate, but even so figuring it out "accurately" is quite difficult.

As RobbieH implies, most estimates are +-20%, which is really as good as you need to be for now. Over time you can refine your estimate by seeing how chemical additions change the level. If chemical additions routinely result in less of a change than you would expect then the pool is larger than you think, and if the changes are routinely larger than you expect then the pool is smaller than you think.

 

[RobbieH]

Exactly. Mine calculated out 47,500 gallons. I noticed my chems were having a more pronounced effect than expected, so I adjusted my volume down until the chems worked out right.

 

[WiseguyFish]

JasonLion,

Yes. The walls are verticle going down 3', then sloping down to 8'. If you look straight down in the deep end, it almost looks looks like you are staring into the open end of a cube, with exaggerated perspective. The only curve is the accent curve in the shallow end, it stretches the entire width of 18' and adds 30" of length at the top of the curve.

 

[WiseguyFish]

Crook,

I dont have any pics yet. They are still working a few kinks out of the liner at the stairs. Hopefully it will be ready to complete the filling this afternoon.

Robbie,

I ran my pool through the pool calculator and it (by the average) calc'ed me to 30,000 gallons.

 

[JasonLion]

Alright, then I would lean towards the high end of my first estimate, 24,000 to 25,000.

30,000 assumes the walls are vertical all the way down.

 

[CaOCl2]

When there's no more sun take a free chlorine reading with FAS-DPD (combined must be 0), add a measured amount of chlorine source to the pool (for example 500 grams of 65% cal hypo), let it circulate thoroughly and measure the increase in free chlorine. Work out the math to give you the volume.