Calculating pool water volume

I believe the calculation for determining the volume of water in a rectangular pool is Length x Width x Avg Depth x 7.5 (someone please correct me if I am wrong).

My question is, how do I determine what my average depth is? I have an 18x42 vinyl inground with a 3' shallow end that goes down to 8 or 8.5' in the hopper.

Thanks!

Just averaging the shallow and deep end depths is usually close enough. In your case, (3 +8)/2= 11/2= 5.5 or (3+8.5)/2=11.5/2=5.75.

So if the deep end is 8 feet you have, 18*42*5.5*7.48=31,101 gallons.
While if it's 8.5 feet you have, 18*42*5.75*7.48=32,515 gallons.

Honestly, you can probably just use 30,000 for simplicity's sake and be just fine.

Thanks Kurt - that's been what I've been assuming. Appreciate the confirmation!