Loan Pool Volume Estimator
Every chemical dose, heater size and filter schedule starts with one number: how much water is in the pool. Pick the shape, enter the dimensions and the shallow/deep depths — get gallons.
Average depth for a sloped-bottom pool is (shallow + deep) ÷ 2 — a 3-ft shallow and 6-ft deep end average 4.5 ft. Constant-depth and above-ground pools just use their wall depth minus a few inches of freeboard.
How it works
Rectangles are length × width × average depth. Circles use π × radius2 × depth; ovals use length × width × π ÷ 4 × depth (the ellipse area). Cubic feet convert to US gallons at × 7.48052. The average-depth convention — (shallow + deep) ÷ 2 — assumes a steady slope; pools with a sharp deep-end drop-off hold a little less than the formula says, and beach entries hold less still, which is why chemical dosing always ends with a water test rather than blind faith in any volume figure.
Formula & worked example
Formula: Rectangular: L × W × average depth. Round: π × (diameter ÷ 2)² × depth. Oval: L × W × π ÷ 4 × depth. Gallons = cubic feet × 7.48052. Average depth = (shallow end + deep end) ÷ 2.
Worked example: A 30 × 15 ft pool averaging 4.5 ft deep: 2,025 cu ft × 7.48052 = 15,148 gallons. An 18-ft round pool at 4 ft averages 7,614 gallons — and weighs about 32 tons of water, which is why above-ground pools want level, compacted ground.
When to use this
- Dosing chlorine, shock or algaecide — every label is written per 10,000 gallons.
- Sizing a pump, filter or heater replacement to the water it must turn over.
- Filling a new pool and predicting the water bill (or the truck loads).
- Comparing salt-system cell sizes, which are rated by pool gallons.
How to use it, step by step
- Pick the shape closest to your pool.
- Measure waterline dimensions, not coping: length and width (diameter if round).
- Set average depth: (shallow + deep) ÷ 2 for sloped bottoms.
- Use the gallon figure for dosing; round to the nearest 500 as labels assume.
- Re-check after any depth-changing renovation — a resurfaced deep end changes the volume.
What the inputs mean
| Input | What it is | Typical values |
|---|---|---|
| Shape | Rectangular, round or oval geometry | Most pools are one of the three |
| Length / diameter | Waterline length; diameter for round | Rect 16–40 ft, round 12–30 ft |
| Width | Waterline width (ignored for round) | 8–20 ft typical |
| Average depth | Mean water depth | 3.5–5.5 ft typical |
Another worked example
An oval pool, 24 × 12 ft at a steady 4 ft average depth (a typical above-ground): the ellipse factor gives 904.8 cu ft — 6,768 gallons. Dosed as a 7,000-gallon pool it behaves; dosed as its 30-ft rectangular cousin it would be chronically over-chlorinated.
Frequently asked questions
How many gallons is a 30 × 15 ft pool?
At a 4.5-ft average depth: 30 × 15 × 4.5 = 2,025 cu ft × 7.48052 = 15,148 gallons. That is the mid-size residential pool most chemical charts are silently written for.
How do I find my pool's average depth?
Add the shallow-end and deep-end depths and halve them. A pool that runs 3 ft to 8 ft averages 5.5 ft — not 8, which is the single most common volume mistake and leads to systematic chemical overdosing.
How many gallons does a round 18-ft pool hold?
π × 9² × 4 ft average depth = 1,018 cu ft ≈ 7,614 gallons. Round above-ground pools are usually shallower than they look — most are 4 ft of water in a 52-in wall.
Why does pool volume matter so much?
Chlorine, shock, algaecide, salt and acid are all dosed per 10,000 gallons. A 20% volume error is a 20% dosing error on everything, forever — it is the cheapest number in pool ownership to get right once.
How long should my pump run?
The rule of thumb is one full turnover per day in season. A 15,148-gallon pool with a 40-gallon-per-minute pump turns over in about 6.3 hours — the volume from this estimator divided by your pump's gallons per minute gives your runtime directly.
💡 What does the pump cost to run?
You have the gallons — the Electricity Cost Calculator turns pump wattage and hours into a monthly running cost.
How many gallons is a 24-ft round above-ground pool?
At 4 ft of water: π × 12² × 4 = 1,810 cu ft ≈ 13,538 gallons. Most '24-ft' pools hold closer to 13,500 than the 15,000+ often quoted from wall height rather than water depth.
Does the volume include the deep-end hopper shape?
The (shallow + deep) ÷ 2 average assumes a steady slope. A hopper bottom (flat deep floor with sloped sides) holds slightly less — roughly 5% under the estimate. For dosing, that error is inside the label's own rounding; for a water-truck order, mention the shape.