Calculate your pool's exact volume in gallons and liters for any shape. Get precise chemical dosing amounts and a full annual maintenance cost estimate.
Chemical dosing is based on your pool volume. Calculate your pool volume first, or enter it manually below.
Estimate your annual pool operating costs — chemicals, electricity, water, and service. Uses your pool volume from Tab 1 or enter manually.
Knowing your pool's exact volume in gallons is the foundation of every pool maintenance decision — chemical dosing, pump run time, heater sizing, and salt system programming all depend on it. The formula varies by pool shape, but all calculations follow the same principle: multiply length × width × average depth × a shape multiplier, then convert cubic feet to gallons (1 cubic foot = 7.48 gallons).
| Shape | Formula | Notes |
|---|---|---|
| Rectangular | L × W × Avg Depth × 7.48 | Most common inground shape |
| Round | Diameter² × 0.7854 × Avg Depth × 7.48 | Above-ground pools, spas |
| Oval | L × W × 0.7854 × Avg Depth × 7.48 | Common above-ground shape |
| Kidney / Irregular | (L1 + L2) / 2 × W × Avg Depth × 7.48 | Measure widths at two points |
| L-Shape | Sum of two rectangles × Avg Depth × 7.48 | Split into two rectangles |
Most residential pools have a shallow end (typically 3–4 feet) and a deep end (6–9 feet for inground pools). To find the average depth, add shallow + deep end depths and divide by 2. For a pool that's 3.5 ft shallow and 8 ft deep: average depth = (3.5 + 8) ÷ 2 = 5.75 ft. For a more accurate calculation on pools with a gradual slope through the middle, use the formula: average depth = (shallow depth + deep depth) × 0.45 instead of dividing by 2 — this accounts for the fact that most of the pool's volume is in the shallower section.
| Pool Type | Typical Dimensions | Gallons | Classification |
|---|---|---|---|
| Hot tub / Spa | 7×7 ft, 3.5 ft avg depth | 300–500 | Small |
| Above-ground round | 18 ft diameter, 4 ft deep | 7,600 | Small |
| Above-ground oval | 15×30 ft, 4 ft deep | 14,000 | Medium |
| Small inground | 12×24 ft, 5 ft avg | 10,800 | Small |
| Average inground | 16×32 ft, 5.5 ft avg | 21,000 | Medium |
| Large inground | 20×40 ft, 6 ft avg | 36,000 | Large |
| Competition lap pool | 25×75 ft, 7 ft deep | 98,000 | Commercial |
Every pool chemical — chlorine, shock, algaecide, pH adjusters, cyanuric acid — is dosed per 10,000 gallons. A 15,000-gallon pool requires 1.5× the dose of a 10,000-gallon pool. Getting this wrong doesn't just waste money — under-dosing chlorine leads to algae blooms and cloudy water; over-dosing can irritate eyes and skin and damage pool surfaces and equipment. The single most common cause of pool chemistry problems is not knowing the pool's actual volume.
Your pool pump needs to turn over the entire pool volume at least twice every 24 hours — this is called the "turnover rate." To find the minimum pump flow rate: divide your pool volume by 12 (hours) to get the required gallons per hour, then divide by 60 to get gallons per minute (GPM). For a 20,000-gallon pool: 20,000 ÷ 12 = 1,667 GPH ÷ 60 = 27.8 GPM minimum. Always size up to account for resistance from filters, heaters, and plumbing. A 1.5–2 HP pump is typical for 15,000–25,000-gallon pools.
Variable speed pumps are required by law in many states and pay for themselves within 1–3 years through electricity savings. Running at lower speeds (1,200–1,800 RPM instead of 3,450 RPM) reduces energy use by 60–80% while still achieving adequate turnover — just over longer periods. Most variable speed pumps have built-in timers that run high speed for 2–4 hours for cleaning cycles, then drop to low speed for the remaining 6–8 hours.
Sand filters are the most common and lowest maintenance option. They filter particles down to 20–40 microns and need backwashing every 1–4 weeks. Size your sand filter so the flow rate doesn't exceed the manufacturer's maximum — usually 15–20 GPM per square foot of filter area. Cartridge filters filter to 10–15 microns and need cleaning 2–4 times per season (no backwashing needed). They're ideal for areas with water conservation restrictions. DE (diatomaceous earth) filters are the most effective, filtering down to 2–5 microns, giving the clearest water — preferred for competition pools and pools with glass or pebble finishes that show debris most easily.
Salt chlorinators are rated by the maximum pool volume they can handle. Always buy a unit rated for 1.5–2× your actual pool volume — this allows the system to run at 50–70% capacity rather than 100%, which dramatically extends cell life. A cell running at full capacity lasts 2–3 years; one running at 60% can last 5–7 years. Most manufacturers offer models at 20,000, 40,000, and 60,000-gallon ratings. For a 15,000-gallon pool, a 20,000-gallon cell is appropriate; a 40,000-gallon cell will last longer but costs more upfront.
| Dimensions (L×W) | 3.5 ft avg | 5 ft avg | 6 ft avg | 7 ft avg |
|---|---|---|---|---|
| 10×20 ft | 5,236 | 7,480 | 8,976 | 10,472 |
| 12×24 ft | 7,540 | 10,771 | 12,925 | 15,080 |
| 14×28 ft | 10,269 | 14,670 | 17,604 | 20,538 |
| 16×32 ft | 13,421 | 19,173 | 23,007 | 26,842 |
| 18×36 ft | 17,000 | 24,286 | 29,143 | 34,000 |
| 20×40 ft | 20,994 | 29,992 | 35,990 | 41,988 |
| 25×50 ft | 32,803 | 46,861 | 56,234 | 65,606 |
Volume in US gallons. Rectangular pool. Formula: L × W × Depth × 7.48. For oval pools multiply by 0.7854. For pools with variable depth, use (shallow + deep) × 0.45 for average depth.
Free chlorine should be maintained at 1–3 ppm (parts per million) in a residential pool. Below 1 ppm, bacteria and algae multiply rapidly. Above 5 ppm, the water becomes irritating to eyes and skin. Chlorine is consumed by sunlight (UV destroys 90% of unstabilized chlorine in 2 hours), swimmer load, debris, and oxidation. Cyanuric acid (stabilizer/conditioner) protects chlorine from UV, extending its effective life by 3–8×. Target CYA levels of 30–50 ppm for outdoor pools using trichlor or dichlor, and 70–80 ppm for saltwater pools.
| Parameter | Ideal Range | Low Effect | High Effect |
|---|---|---|---|
| Free Chlorine | 1–3 ppm | Algae, bacteria | Irritation, bleaching |
| pH | 7.4–7.6 | Corrosion, eye irritation | Scale, cloudy, chlorine loss |
| Total Alkalinity | 80–120 ppm | pH unstable (bouncing) | Scale, cloudy water |
| Calcium Hardness | 200–400 ppm | Corrosion, etching | Scale, cloudy water |
| Cyanuric Acid | 30–50 ppm | Rapid chlorine loss | Chlorine lock (>100 ppm) |
| Salt (saltwater pool) | 2,700–3,400 ppm | Low chlorine generation | Equipment corrosion |
Shocking (superchlorinating) your pool raises chlorine to 10–30 ppm to destroy combined chlorine (chloramines), kill algae, and oxidize organic contaminants. You should shock after heavy bather load (party), after a rainstorm, when water is cloudy, at pool opening, and approximately every 1–2 weeks during the swimming season as a preventive measure. Use 1 pound of calcium hypochlorite (cal-hypo) shock per 10,000 gallons for routine shock. For algae treatment, use 2–3 lbs per 10,000 gallons. Always shock at dusk — sunlight destroys chlorine before it can work.
Pool ownership costs vary significantly by pool size, type, climate, and how much work you do yourself. The biggest variables are electricity (pump and heater), professional service fees, and whether you have a heated pool. Below are typical annual cost ranges for a 15,000-gallon inground pool in the US:
| Cost Category | DIY | With Weekly Service | Notes |
|---|---|---|---|
| Chemicals | $400–$700 | $300–$500 | Lower with service (bulk pricing) |
| Electricity (pump) | $600–$1,200 | $600–$1,200 | Variable speed pump saves 60–70% |
| Electricity (heater) | $0–$2,000+ | $0–$2,000+ | Gas/propane; heat pumps cheaper |
| Service / Labor | $0 | $1,200–$3,600 | $100–$300/month weekly service |
| Opening / Closing | $50–$150 | $400–$800 | Per service |
| Repairs / Parts | $200–$600 | $200–$600 | Annual average |
| Total (DIY) | $1,200–$2,500/year | ||
| Total (with service) | $3,000–$7,000/year | ||