Pool Volume & Chemical Calculator
Calculate how many gallons your pool holds from its shape and depths, then convert any product's per-10,000-gallon dose into the exact amount your pool needs.
Leave at 0 to skip — every product's label specifies its own dose per 10,000 gallons of pool water.
Always follow the product label for chemical dosing and safety handling, and test water chemistry before and after treating — this only converts the label's dose rate to your pool's actual volume.
Every chemical label assumes a number you probably don’t know
Pick up any pool shock, chlorine tablet or algaecide container and the dosing instructions are printed the same way: “X ounces per 10,000 gallons.” That’s useless without knowing your own pool’s actual gallon count, and most pool owners either never calculated it precisely or are working from a rough figure a builder mentioned years ago. This calculator solves the actual bottleneck — turning length, width and the two depths you can measure with a tape measure into gallons, then straight into whatever dose your specific product calls for.
Why average depth, not deep-end depth
A sloped in-ground pool doesn’t hold water at its deep-end depth throughout — it tapers from shallow to deep, so using the deep-end number for the whole pool overstates volume substantially, and using the shallow-end number understates it just as badly. Averaging the two depths approximates the sloped bottom as a flat plane at the midpoint, which is standard practice in the pool industry and accurate enough for both volume estimates and chemical dosing, which itself has a reasonable tolerance band. Above-ground pools with a flat bottom skip this problem entirely — just enter the same value for both depths.
Rectangular versus round geometry
A rectangular or square pool’s volume is straightforward: length times width times average depth, in cubic feet, then converted to gallons. Round and oval above-ground pools use circular geometry instead — area is π times the radius squared (half the diameter you entered), times average depth. Freeform or kidney-shaped pools don’t have a clean formula, but approximating them as the nearest rectangle or oval typically lands within about 10% of the true volume, which is well within the tolerance chemical dosing tolerates.
Cubic feet to gallons: the conversion that’s easy to get wrong
Water volume calculations naturally come out in cubic feet from a length-times-width-times-depth calculation, but every chemical label, pump-turnover spec and water bill is denominated in gallons. The conversion factor is 7.48 gallons per cubic foot — this calculator applies it automatically, but it’s worth knowing if you’re ever doing a rough calculation by hand or checking a contractor’s number: a “20,000 gallon” pool quote should correspond to roughly 2,674 cubic feet of actual water.
Getting dosing right actually matters, not just for cost
Under-dosing chlorine shock doesn’t just mean the pool takes longer to clear — for a genuine algae bloom, a dose that’s too low can fail to break the algae’s chlorine demand entirely, leaving you with green water and a container that’s now half-empty for nothing. Over-dosing wastes money and, for some products, can push pH or chlorine levels into ranges that irritate skin and eyes or bleach liners and pool toys. Getting the gallon figure right once and keeping it on hand — written on the pump housing, saved in your phone — removes the guesswork every single time you treat the water afterward.
What this calculator does not do
This tool converts volume and label doses; it does not test water chemistry, recommend how much chlorine to maintain day to day, or account for the countless product-specific formulations on the market — always follow the actual instructions on whatever product you’re using, since concentration and recommended dose vary by brand and form (liquid, granular, tablet). Test strips or a proper test kit remain the only reliable way to know your pool’s current chemical levels before and after treating. See the water usage calculator if you’re also trying to estimate what filling or refilling the pool adds to a water bill.
How this is calculated
Average depth = (shallow depth + deep depth) ÷ 2 Rectangle: volume (cu ft) = length × width × average depth Round: volume (cu ft) = π × radius² × average depth Gallons = volume (cu ft) × 7.48 Chemical (oz) = gallons ÷ 10,000 × label dose
Frequently asked questions
- How many gallons is my pool?
- Multiply length × width × average depth for a rectangular pool, or π × radius² × average depth for a round one, then multiply by 7.48 to convert cubic feet to gallons. Average depth is the shallow-end depth plus the deep-end depth, divided by two — this calculator does all of it from the four numbers on a pool spec sheet or a tape measure.
- Why do I need to know my pool's exact volume?
- Nearly every pool chemical — chlorine, shock, algaecide, pH adjusters — is dosed per 10,000 gallons on the product label. Guessing your pool's size high wastes chemical and money; guessing low under-treats the water, which for shock treatment specifically can mean the difference between actually breaking an algae bloom and just diluting it.
- Is an above-ground pool calculated differently than in-ground?
- No — the geometry math is identical for both. Above-ground pools are usually round or oval with a flat bottom, so enter the same value for shallow and deep depth; in-ground pools more often slope from a shallow end to a deep end, so use the actual two depths.
- What if my pool is an odd shape, like a kidney or freeform?
- Approximate it as the closest rectangle or oval and you'll typically land within about 10% of the true volume — close enough for chemical dosing, which has built-in tolerance. For a truly precise number on an irregular shape, most pool professionals estimate by adding up simpler sub-shapes.