Hi, I have an inground spa which we use as a pool and do not heat. I have had trouble calculating the size mostly because of the wrap-around bench, which in turn makes adding the correct amount of chemicals tricky. I have attached a photo. Outside dimensions are 122” x 76”. Depth to middle is 48” and depth to wrap-around seat is 24”. I appreciate any help.
- Jul 21, 2013
- 52,972
- Pool Size
- 35000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
There is a Chemical Way of Calculating Pool Volume using an alkalinity test kit, sodium bicarbonate or acid, and the formula.
DrewLG
Gold Supporter
For accuracy we'd really need the actual dimensions of the inner (deep) section and the stair sizes, but from just eyeballing the photo I'll assume that the bench is 20" deep all around. That makes the deep section 82 x 36 inches. The bottom step looks like 18 x 36 x 6 and the top step looks like 9 x 18 x 6.
If we ignore the stairs for now, the volume is 122 x 76 x 24 cubic inches for the upper 24" of water, plus 82 x 36 x 24 cubic inches for the lower 24" of water.
That's 293376 cubic inches. Stair volume is (18 x 36 x 6) + (9 x 18 x 6) = 4860 cubic inches, so total water volume is 293376 - 4860 = 290460 cubic inches, or 168 cubic feet.
There are 7.48 gallons in a cubic foot, so the volume in gallons is 168 x 7.48 = 1257 gallons.
The 1257-gallon result is an approximation based on the assumptions I made about stair and bench sizes. And it's always best to guess low and later adjust upward if necessary (because underdosing with chemicals is easier to correct than overdosing). So I would round down to 1200 gallons and see whether that number gives you a good match between predicted and actual chemical results.