Oval Pool Gallons Calculator (True Oval vs Above Ground)

Calculator: ellipse or straight-sided oval

For example, 30 × 15 ft at 5 ft deep is 15,025 gallons straight-sided but 13,219 gallons as an ellipse. Pick the shape that matches yours, and the calculator does the rest.

How to tell which you have: look along the long side. If there's a straight stretch of wall between two curved ends, choose "Straight sides, round ends". Above-ground ovals are built this way. If the wall curves continuously with no straight section, like a stretched circle, choose "True ellipse". For above-ground pools, enter the wall height. The calculator assumes 90% fill and applies the usual frame-pool correction. For inground pools, enter the water depth at both ends.

Why the two formulas differ (30 × 15 × 5 ft: 13,219 vs 15,025 gal)

An ellipse's area is π/4 × length × width. A straight-sided oval is a rectangle of (length − width) × width plus a full circle with a diameter equal to the width, split into two half circles at the ends. At the same length and width, the straight-sided shape fills out the "corners" that an ellipse cuts off.

True ellipse, 30 × 15 ft, 5 ft deep: π/4 × 30 × 15 × 5 × 7.48 = 13,219 gallons.
Straight sides and round ends, same size: (15 × 15 + π/4 × 15²) × 5 × 7.48 = 15,025 gallons.

That's 13.7% more water. If you dose a straight-sided pool as an ellipse, every chemical amount comes out about 12% short. Chlorine you expect to give 3 ppm gives about 2.6. For a 2:1 oval, the gap is always 13.7%. It is smaller for ovals closer to round and larger for longer, narrower ones (an 18 × 40 ft oval differs by 15.0%).

Chart: common oval sizes

Gallons at 4 ft of water for both shapes. For above-ground ovals by wall height (48, 52, and 54 in), use the above-ground gallons chart.

Oval pool gallons at 4 ft average water depth
Size	Straight sides, round ends	True ellipse	Difference
12 × 18 ft	5,538	5,076	9.1%
12 × 24 ft	7,693	6,768	13.7%
15 × 24 ft	9,327	8,460	10.2%
15 × 30 ft	12,020	10,575	13.7%
16 × 32 ft	13,676	12,032	13.7%
18 × 33 ft	15,693	13,959	12.4%
21 × 41 ft	22,931	20,234	13.3%

US gallons, exact geometry. For another depth, scale linearly: at 5 ft, multiply by 1.25. Above-ground frame pools typically hold about 7% less than the geometry of their nominal size.

Where the 6.7 multiplier comes from

You'll often see "oval gallons = length × width × depth × 6.7". Hayward uses that factor. It isn't a law of geometry. It is what a straight-sided oval works out to when the length is twice the width: (1 + π/4) ÷ 2 × 7.48 = 6.68. The factor changes with the proportions:

length = width (a circle): 5.88, the same as an ellipse;
length = 2 × width: 6.68, hence 6.7;
length = 3 × width: 6.95;
very long and narrow: approaches 7.48, a plain rectangle.

A true ellipse always uses 5.88 (often rounded to 5.9, the same as a round pool). So 6.7 is a good shortcut for a 2:1 straight-sided oval, a small overestimate for shorter ones like 12 × 18 ft (6.41), and wrong for a real ellipse. The calculator uses the exact formula for any proportion. For rectangles, kidneys, and L-shapes, use the pool volume calculator.

FAQ

How many gallons is my oval pool?

For a straight-sided oval: ((length − width) × width + 0.785 × width²) × average depth × 7.48. For a true ellipse: length × width × depth × 5.9. A 15 × 30 ft straight-sided oval with 4 ft of water holds 12,020 gallons.

How to calculate oval pool gallons?

Measure length and width inside the wall and the average water depth in feet. Decide whether the long sides are straight. Then use the matching formula above, or enter the numbers in the calculator.

Sources

Hayward, pool volume rule of thumb (L × W × D × 6.7 for ovals), as summarized in our engine research; formulas on our methodology page