Triangular Pool Volume Calculator

Select Imperial or Metric at the top of the input panel. Imperial shows results in US gallons and cubic feet; Metric shows litres and cubic metres.

Enter your pool dimensions:

1. Base (B) — the longest straight wall of the triangle. Measure inner surface to inner surface at the waterline, not along the top coping.
2. Height (H) — the perpendicular distance from the base wall to the opposite corner. This is measured at a right angle to the base, not along the angled pool wall.
3. Shallow End — water depth at the shallowest point, measured from the waterline to the pool floor.
4. Deep End — water depth at the deepest point. For a flat-bottom pool, enter the same value as the Shallow End.

Results display in US gallons, litres, and cubic feet. Use the volume for chemical dosing, pump sizing, or water-change planning.

If you already know the exact surface area from a builder's plan or survey, expand the I Know My Pool's Surface Area panel below the main inputs. The 0.5 factor is not re-applied when you enter a measured area directly.

The perpendicular height of a triangular pool is rarely the same as the length of either angled wall — it is always shorter, and using the angled wall length instead will overstate the volume.

Triangular pool volume is the total amount of water the pool holds when filled to its normal waterline. It is measured in US gallons, litres, or cubic feet. The number depends on three measurements: the base wall length, the perpendicular height from that base to the opposite corner, and the average water depth.

Accurate volume matters because chemical dosing, filtration pump sizing, and water-change scheduling all depend on how many gallons or litres are in the pool. Triangular pools are less intuitive to estimate than rectangular pools because the water surface area depends on both the base and the perpendicular height — not simply two side lengths multiplied together. The pool volume formula guide explains how these geometric calculations work across different shapes.

Triangular pools range from compact corner installations with a 10 ft base to large architectural features with a 30 ft base or more. A small triangular pool at 10 ft × 8 ft × 5 ft average depth holds about 1,496 gallons (5,663 L), while a larger 24 ft × 16 ft pool at the same depth holds 7,181 gallons (27,184 L) — nearly 5× more water from a relatively modest increase in dimensions.

Two triangular pools with similar slant-wall lengths can hold different water volumes if the perpendicular height differs. A pool where the apex sits far from the base has a greater perpendicular height — and more water surface area — than one where the apex is close to the base, even if the wall lengths are identical.

The most reliable approach is to measure the actual base and perpendicular height inside the pool at the waterline and enter those into the calculator. Visual guessing tends to overestimate volume because people unconsciously treat the triangle as a rectangle.

Triangular pools use the same half-base-times-height principle as any triangle in geometry. A triangular pool holds exactly half the water of a rectangular pool with the same base, perpendicular height, and depth — the 0.5 factor accounts for this difference. The same principle applies to L-shaped pools where triangular sub-sections appear as part of a larger layout.

The 0.5 factor is the triangle area constant. A triangle is exactly half of the rectangle formed by its base and perpendicular height. The calculator applies this factor as a named constant (0.5), not a rounded approximation.

Height in this formula means the perpendicular height — the straight-line distance from the base wall to the opposite corner, measured at a 90° angle to the base. It is not the length of either angled wall. Using the slant wall instead of the perpendicular height overstates the surface area and inflates the volume.

Average depth is the midpoint of the shallow and deep end measurements: (Shallow + Deep) ÷ 2. Keep all measurements in the same unit system — mixing feet and metres will produce an incorrect result.

A triangular pool with a 20 ft base, 16 ft perpendicular height, 3.5 ft shallow end, and 6.5 ft deep end:

This mid-size triangular pool holds about 5,984 gallons (22,653 L). A rectangular pool with the same 20 ft × 16 ft footprint and 5 ft depth would hold twice as much — roughly 11,969 gallons (45,306 L) — which is why the 0.5 factor matters.

The base is the longest straight wall of the triangle, measured from inner surface to inner surface at the waterline. Do not use the top coping or outside tile edge — measure the water-holding dimension at the water surface.

The perpendicular height is not the length of either angled wall. It is the straight-line distance from the base wall to the opposite corner, measured at a right angle (90°) to the base. The slant wall follows the angled edge and is always longer than the perpendicular height. Using the slant wall length instead of the perpendicular height is the single most common measurement error on triangular pools — it overstates the surface area and inflates the calculated volume by 10 to 30 percent depending on the triangle shape.

Measure the water depth at the shallowest and deepest points of the pool, from the waterline down to the pool floor. Average depth equals (Shallow + Deep) ÷ 2. If the pool has a flat bottom, enter the same value in both depth fields.

For pools with an uneven slope or a step, measure three or four depth points along the centre line and average them. The calculator uses a two-point average, so entering the true shallow and deep extremes gives the best straight-line approximation.

Calculated using ½ × base × perpendicular height × depth. 1 cu ft = 7.48052 US gal = 28.3168 L. Average depth = 5.0 ft unless noted otherwise. Height is the perpendicular height — not the slant wall.

The smallest pool in this table holds 1,496 gallons (5,663 L), while the largest holds 13,465 gallons (50,970 L) — a 9× difference. That gap directly affects how much chlorine to add, what size pump to install, and how long a water change takes. For broader comparisons across different pool shapes, see the pool volume by size reference. For your exact dimensions, use the calculator above.

Chlorine and other chemical doses are calculated by water volume. A triangular pool holding 6,000 gallons (22,712 L) needs exactly half the chlorine of a rectangular pool holding 12,000 gallons (45,425 L) with the same footprint dimensions. Overdosing can cause skin and eye irritation; underdosing leaves the water undertreated. Always follow the product label and your pool equipment specifications for your exact pool setup. For volume-based dosing reference, see the chemical dosing guide.

Filtration pump sizing depends on total water volume. Most residential pools require the pump to turn over the full volume at least once every 6 to 8 hours. A 6,000-gallon (22,712 L) triangular pool needs a pump rated for at least 12.5 gallons per minute (GPM) to complete one turnover in 8 hours. Using a volume estimate that is too high leads to an oversized pump that wastes energy; an estimate that is too low leads to poor water circulation.

Water-change planning is simpler when you know the exact volume. A 6,000-gallon (22,712 L) pool at a typical garden hose flow of 10 gallons per minute takes roughly 10 hours to refill. Draining a partial volume — say 25 percent for a seasonal refresh — means replacing about 1,500 gallons (5,678 L), which takes approximately 2.5 hours.

Triangular pools are easier to mis-measure than rectangles because the perpendicular height is not visually obvious. A measurement error of 2 ft on the perpendicular height of a 20 ft × 16 ft pool changes the volume by about 748 gallons (2,832 L) — enough to shift a chlorine dose by roughly 12 percent. The pool volume formula guide covers how to avoid these compounding errors across shapes.

1. Using the slant wall length instead of perpendicular height. The angled wall of a triangular pool is always longer than the perpendicular height from the base to the opposite corner. Entering the slant wall length into the Height (H) field overstates the surface area by 10 to 30 percent. Measure perpendicular height at a 90° angle to the base — not along the pool wall.

2. Measuring outside dimensions instead of inside water-holding dimensions. Coping, tile, and structural walls add several inches to each side. The calculator needs the internal water dimensions measured at the waterline, not the outside footprint from a site plan.

3. Guessing the triangle shape instead of measuring base and height. Triangular pools come in many proportions. A long, narrow triangle holds less water than a wide one with the same base, even if they look similar from a distance. Always measure the actual perpendicular height rather than estimating by eye.

4. Mixing feet and inches incorrectly. A 20-foot base is 240 inches, not 20 inches. If the calculator expects feet, entering 240 would overstate volume by a factor of 12. Double-check whether your measurement is in feet, inches, or metres before entering values.

5. Using a single depth point on a sloping floor. Many triangular pools slope from a shallow end to a deep end. Using only the deep-end measurement overstates water volume; using only the shallow end understates it. Enter both the shallow and deep measurements so the calculator can average them correctly.

6. Assuming a corner-cut pool works like a simple triangle. Some pools are described as "triangular" but have one or more curved walls or clipped corners. If any wall is curved, the half-base-times-height formula underestimates or overestimates the true area. For freeform shapes, use the I Know My Pool's Surface Area mode with a measured or surveyed area instead.