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Thread: HOW MANY GALLONS?

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    HOW MANY GALLONS?

    HOw many gallons of water would be in my pool? I have had several estimates given by pool people and wonder which is correct.

    18 ft round 52 inches

    thanks,
    waterbug
    18 ft.52" Round Atrium AG -7600 gallons, Sand Filter, Vinyl liner, Royal Entrance Steps, 80 lbs.solarsalt

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    SeanB's Avatar
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    Well, none of the online calculators seem to agree, but the average seems to be around 7,000- 7,500 gallons.

    Was there any documention with the pool that might say the volume?
    TFP Founder

    My Pool: 13K gal IG gunite with 7' spa, Pentair Cartridge Filter, Intellichlor IC40 SWG, Polaris 280 Cleaner, TF-100 Test Kit w/ salt test.

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    divnkd101's Avatar
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    OK. If I have done my calcs correct, I come up with roughly 8247 gallons. I am sure there are other math wizards on the forum as well if I am not correct. Good Luck

    Volume of a cylinder = pi * radius2 * height
    where pi (Ï€)=3.1415926535 ...
    MIKE

    21K Inground Custom w/ Spa (Gunite/Plaster), SWCG, Hayward Northstar, Polaris 280, Hayward Color Logics, Jandy PS-8

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    Using the formula for a round pool as diameter X diameter X av depth X 5.9

    18 X 18 = 324
    324 X 4 = 1296 (4' av depth is probably a little high, but it makes for easier calculations :P )
    1296 X 5.9 = 7646.4 (with a 4' depth Bleachcalc 262 gave me 7633.44 - close enough for me!) (the difference is that Micheal used 5.89 as the multiplier instead of my 5.9 - I'm sure his is more accurate)

    I assume that the purpose of wanting to know is for adjusting the chems. If you use 7500 as the gallonage, you should be close enough.

    **a note on adding chems**
    It is a good idea to add the chems in 2 or 3 doses (letting the system run for a few hours before retesting), as opposed to all at once- the reason being that the dosing tables and gallon estimates can be wrong, it's easier to add a little more of whatever chem later than to have to use another chemical to reduce an overshot mark.
    Luv& Luk
    -Ted

    Having done construction and service for 4 pool companies in 4 states starting in 1988, what I know about pools could fill a couple of books - what I don't know could fill a couple of libraries :-D

    POOL SCHOOL, TF Testkits, Jason's Pool Calculator, CYA vs. cl chart, (Just a few DARNED handy links!)

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    divnkd101's Avatar
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    OK, yeah duh!!!! Well at least now you know how many gallons it will take before your pool begins to overflow... ha ha ha. I used 52 inches as the depth. Thanks waste.
    MIKE

    21K Inground Custom w/ Spa (Gunite/Plaster), SWCG, Hayward Northstar, Polaris 280, Hayward Color Logics, Jandy PS-8

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    Okay thanks, this sounds about right to me according to what the pool installer told us. I asked a chemical guy on Saturday how much of .....we would need - how many gallons was our pool etc. and he told me 15, 000 and that just didn't sound right to me.........I am beginning to understand "Pool stored" very well.

    Thanks eveyone!
    18 ft.52" Round Atrium AG -7600 gallons, Sand Filter, Vinyl liner, Royal Entrance Steps, 80 lbs.solarsalt

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    Hey that's cool, thanks! Did it the first time and got 30000 or so, because i did the radius 18ft, instead of 9.....duh!

    Very nice tool!
    18 ft.52" Round Atrium AG -7600 gallons, Sand Filter, Vinyl liner, Royal Entrance Steps, 80 lbs.solarsalt

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    gonefishin's Avatar
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    Hi waterbug,

    I don't like this pool calculator as well as the BleachCalc, but this is easy to use if you don't have the bleachcalc program.

    dan
    21' Aqua-Leader AGP (10,200 gallons).
    Hayward cartridge filter and two speed pump.
    Aqua-Cal HeatWave 100k (HeatPump)
    Salt 3200ppm (in non-salt water pool)
    Borates 20ppm (slowly raising)
    Aqua-Rite SWG

  10. Back To Top    #10
    I was fascinated by this formula for capacity of round pools: D^2*H*5.9

    Since I'm used to PI*R^2*H *7.48 I was intrigued.

    OK: We all know the formula for the area of a circle is PI*R^2 ("Pie are squared").

    Volume means multiplying by the height, in feet. This give you the volume in cubic feet...useless.

    But there are 7.48 gallons in a cubic foot.

    But Dee-squared Times Height time 5.9 seems weird--it's not.

    You see, D^2 is ALWAYS 4 times greater than R^2, no matter the value of R. See, D^2 = (R*2) * (R*2) because D=R*2. Simplifying the right side gives: R^2*4 !

    So there are now 3 constants: PI--(3.14159.....), 7.48 (gal/cube foot) and 4--the relation between the squares of the diameter and radius.

    Multiply PI by 7.48 and divide by 4 to get one constant....

    ET VOILA! Approx. 5.9!

    So Multiply the square of the diameter, times the height and then by 5.9 and you have a PERFECT calculation of the gallonage of a round pool.

    Use this on ovals too...an oval is merely a round that's been cut into 2 halfs with a straight section in the middle..That middle is a rectangle where the width is ALWAYS the same as the diameter. The length of the rectangle is the FULL length of the pool less the diameter. L*W*H*7.48 equals the gallons in the middle. Add that to D^2*H*5.9 and you have your oval figured almost as quickly!

    Example: Say you have an 18X33 oval where the water is 4' deep (water, not the walls). The calculation is simple:
    1) The two semi circles at each end are really an 18' circle, cut in half:
    18*18*4*5.9=7646.4 gallons.
    2) the width of the pool is 18', right?
    3) the length of the center rectangle is .... 33' - 18', right? That's 15'
    4) The rectangle is 18*15*4*7.48 (Gal/cub ft). = 8078.4 gallons.
    5) 7646.4 + 8078.4 = 15724.8 gallons

    But you can use 16,000 for most figuring. Or if it's lower you may use 15,000 gallons.
    Stay ahead of your water!

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    In the Industry

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    Man, you guys get way to deep for my head. For thirty years now an 18' by 48" pool has held 7500 gallons of water. My guess would fall in the 8200 range.

    I have not seen this kind of math since high school.

    Later, Dennis
    Pro pool installer for over 35 years
    Shadebuilder.com

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    Hijacking:

    Welcome, Dennis!

    That is all. 8)

    8000 gallon 20' x 48" round vinyl frame pool, 12" sand filter (don't have the specs on the pump), TF100 test kit
    Handy Links: PoolMath, TF-100 Test Kit, Pool School, CYA-Chlorine Chart
    "Shock" is a process, not a product!

  13. Back To Top    #13
    Quote Originally Posted by Dennis
    Man, you guys get way to deep for my head. For thirty years now an 18' by 48" pool has held 7500 gallons of water. My guess would fall in the 8200 range.

    I have not seen this kind of math since high school.

    Later, Dennis
    Nope, 7646 by the D-Squared-H-5.9 formula, 7614 using Pi. 7500 gallons is MORE than good enough... (unless you have to carry those extra 114-146 gallons! that's 975 - 1250 lbs of water... )
    Stay ahead of your water!

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    NWMNMom's Avatar
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    I like to sit back and watch you all do the math for me!
    18x33x52 Buttressfree Seaspray (Wilbar) AGP - 1.5hp Pentair Maxim w/22" Pentair Meteor Sand Filter, Aqua Rite SWG System, Biltmore Walk In Steps - 2/4x20 Solar Panel Setup - Doheny Jet Drive (RIP -Pool Rover Jr) - finally hard plumbed the whole darned thing -
    Beats Driving to the Lake!

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    Dennis, you're making the same mistake that divnkd made in that you are taking the highth of the wall to be the water depth, the water is ~6 - 9 " below the top of the wall.
    Luv& Luk
    -Ted

    Having done construction and service for 4 pool companies in 4 states starting in 1988, what I know about pools could fill a couple of books - what I don't know could fill a couple of libraries :-D

    POOL SCHOOL, TF Testkits, Jason's Pool Calculator, CYA vs. cl chart, (Just a few DARNED handy links!)

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    Hi waste, I am not doing any math here so making a mistake would be a little difficult. My fiqure came from an installation manual I read over twenty years ago.

    I was however going ask Carl that same question. Did you allow for two inches of sand, a six inch cove and the water level a few inches down from the top of the pool. Would that get it closer to 7500 ?
    Pro pool installer for over 35 years
    Shadebuilder.com

  17. Back To Top    #17
    Quote Originally Posted by Dennis
    Hi waste, I am not doing any math here so making a mistake would be a little difficult. My fiqure came from an installation manual I read over twenty years ago.

    I was however going ask Carl that same question. Did you allow for two inches of sand, a six inch cove and the water level a few inches down from the top of the pool. Would that get it closer to 7500 ?
    Dennis, I ALWAYS consider the WATER level, not the wall height. I never thought about the cove (the angle would be fun to figure in--must be a twist on the volume of a cone--but I'm WAGging it that it would mean no more than 1%, if even that.). By using the water level, you don't need to figure the 2" of sand--it's already there. Normally, if the WALL is 4', I assume a water level of 3.5'. But I also assume if someone tells me the water depth is 4', it's 4'. Just like I assume if they tell me the diameter is 18', it's 18', not 17' 6".

    Still, if you are within 100 gallons on a 7600 gallon pool, it's not going to screw up you chemical calculations. In fact, it's my contention that if you are off by 5% either way it's TOTALLY irrelevant, and if you are off by 10% either way, it's probably not going to matter much.

    Thoughts on calculating the cove (see what you started! ):
    Assume it's 45 degrees, 6" high, and 6" wide.

    Let's start by computing a washer shape around the pool that's 6"x6" on the bottom edge, where the cove goes. Yeah, it's got a square profile. I know. Just wait.

    Now compute a pool that 18' by 6" and another that's 17' by 6". Using D^2*H*5.9 we get 956gal(18') - 853 gal(17') = 103 gallons for the 6"HxW ring around the pool for the cove. Why 17'? because our washer shape is 6" wide--and it's on both sides of the pool, so you double it to 1'. Thus 17'.

    Now, since the cove is a diagonal, it has half of that volume, or 51.5 gallons. I certainly wouldn't worry about that in calculating a 7600 gal pool
    Stay ahead of your water!

  18. Back To Top    #18

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    Carl, thanks for the extra math ! I've just always used the diameter ^2 * av depth * 5.9 because it happens to work for estimating gallonage, when dosing a pool.
    Another thing I'd like to point out is that the desired range for any pool chemical parameter is forgiving enough that if you have a good estimate of the gals., you can get away with a little 'slop' in the actual gallonage. (there are no 'magic' or 'perfect' numbers to keep the pH, alk, or any of the other #s at - as long as they 'all play well together' and none are too far out of range, the water will be fine!)
    Luv& Luk
    -Ted

    Having done construction and service for 4 pool companies in 4 states starting in 1988, what I know about pools could fill a couple of books - what I don't know could fill a couple of libraries :-D

    POOL SCHOOL, TF Testkits, Jason's Pool Calculator, CYA vs. cl chart, (Just a few DARNED handy links!)

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