Pool Gallon Calculator

How to use this calculator

1. Pick your pool shape. Six modes — rectangle (the most common in-ground / above-ground shape), round (above-ground Intex / Bestway / Doughboy), oval (above-ground or in-ground), kidney (curved residential), L-shape (in-ground with appendage), and freeform (irregular / lagoon). Each shape uses the correct geometric formula automatically.
2. Choose depth mode. "Sloped" supports a shallow end + deep end (the normal in-ground case — most pools have a slope between the two). "Uniform" uses a single average depth (the normal above-ground / Intex case).
3. Enter dimensions in feet. For rectangles, length × width. For round, diameter. For oval, length × width (the longer + shorter axes). For kidney, length × wide-width + narrow-width. For L-shape, the two rectangles that make up the L. For freeform, the bounding-box length × width — the calculator applies an 85% irregular-shape factor.
4. Pick your hose and pump. ½″ garden hose (~5 gpm) fills slowly; 5/8″ (~9 gpm) is the most common; ¾″ (~17 gpm) is heavy-duty. For drain, a 1/3 HP submersible runs ~30 gpm, 1/2 HP ~50 gpm, 3/4 HP ~70 gpm at typical residential head — these are the workhorse sump-pump ratings.
5. Update your water cost. US urban combined average is ~$5 per 1,000 gallons but the spread is wide (some cities are $3; some California and Texas markets hit $12+). Check your utility bill for the exact figure — refill costs scale linearly so a 3× rate is a 3× bill.
6. Read the result. Gallons headline, with liters + cubic meters + surface area chips. Fill time, drain time, and refill cost row. Start-up chemical doses for a fresh fill (liquid chlorine, stabilizer / CYA, and salt for SWG cell pools). Plus a benchmark line that anchors your number against typical pool sizes.
7. Save the plan. The "Volume + maintenance PDF" button generates a branded one-page PDF with shape, dimensions, all outputs, and the chemical doses. The "Share link" button copies a URL with your exact configuration encoded — open it on a phone or send to your pool builder.

Why this pool gallon calculator is different

After fetching the top 10 SERP results for the same suburban 32×16 pool (slope 3-8), here's what's typical online versus what this calculator adds:

• Most calculators stop at gallons. Pentair, Swim University, The Pool Nerd, Royal Swimming Pools, swimmingpool.com — all give you a volume number and stop. The actual pool owner asking "how many gallons" is asking it for a reason: to size a sump pump (drain), plan a refill (fill time), budget the water bill (cost), or order chemicals (start-up doses). This calculator pre-answers all four downstream questions on the same page.
• Nobody shows drain time by sump pump GPM. A 1/3 HP submersible drains ~30 gpm; 1/2 HP ~50 gpm; 3/4 HP ~70 gpm. For a 15,000-gal pool that's 5 hr vs 3 hr vs 2 hr — which determines whether a winter close-down is an afternoon or a half-day. None of the top 10 surfaces this. We do — and it's the natural upsell to a proper sump pump instead of borrowing your neighbor's hose-bib pump.
• Nobody shows fill time by hose GPM. For a 15,000-gal fresh fill, a ½″ hose takes ~50 hours, 5/8″ takes ~28 hours, ¾″ takes ~15 hours. Multi-day fills mean you start Friday afternoon to swim Monday. None of the SERP top 10 calculates this. We do.
• Nobody shows refill cost. US average urban combined water + sewer is ~$5 per 1,000 gal — that's $75 for a 15K-gal full fill in most markets, but $180+ in California and Texas's drought-tier markets. Real number, real budget. None of the SERP top 10 surfaces this. We do.
• Nobody handles sloped depth on every shape. Most calculators ship "shallow + deep" on rectangles only and force "average depth" everywhere else. Sloped depth is the dominant in-ground pool geometry on every shape — rectangle, kidney, L, freeform. This calculator supports it everywhere.
• Nobody outputs chemical start-up doses. Pentair and HTH gate this behind separate calcs; the others don't have it at all. A freshly-filled pool needs ~3 oz of liquid chlorine per 1,000 gal to reach a 3 ppm Free Chlorine target, ~4 lb of CYA stabilizer per 10,000 gal to reach a 30 ppm baseline, and (for salt-chlorinator pools) salt to hit 3,200 ppm. We ship all three inline.
• Nobody offers an embed. If you write about pools, run a pool-service blog, sell sump pumps, or moderate /r/pools or /r/swimmingpools, the iframe at the bottom of this page lets you host the same calculator with attribution. Free.

How it works (the math behind the numbers)

The core conversion is the same one every pool calculator uses — cubic feet × 7.4805 gives US gallons (NIST conversion). The shape-specific area formulas are standard residential-pool industry:

Conversion: 1 cu ft = 7.4805 US gallons = 28.3168 L

Average depth (every shape):
  avg_depth = slope ? (shallow + deep) / 2 : avg_depth_input

Per-shape volume (cu ft):
  Rectangle:   L × W × avg_depth
  Round:       π × (D/2)² × avg_depth
  Oval:        (π / 4) × L × W × avg_depth      // ellipse area × depth
  Kidney:      0.45 × (W_wide + W_narrow) × L × avg_depth
  L-shape:     (L1 × W1 + L2 × W2) × avg_depth   // two rectangles
  Freeform:    L × W × avg_depth × 0.85          // bounding box × 0.85

Fill / drain / cost:
  fill_hours  = gallons / hose_gpm / 60
  drain_hours = gallons / pump_gpm / 60
  refill_cost = gallons × ($ per 1000 gal) / 1000

Start-up chemicals (fresh, unsanitized fill):
  liquid_chlorine_oz = gallons / 1000 × 3       // raises FC ~3 ppm at 12.5%
  stabilizer_lb      = gallons / 10000 × 4      // brings CYA to ~30 ppm
  swg_salt_lb        = gallons × 3200 × 8.345e-6 // raises NaCl to ~3,200 ppm

Cubic feet to gallons is the NIST conversion: 1 cu ft = 7.4805194805 US gallons (NIST General Tables of Units of Measurement). Same number every legitimate pool calculator uses; some round to 7.5 for simplicity.

Oval area uses the ellipse formula π/4 × L × W (the major and minor axis halves). This matches what Swim University, The Pool Nerd, and most pool engineering references publish.

Kidney coefficient 0.45 is the residential pool-industry standard. The kidney is geometrically tricky — somewhere between an ellipse and a rectangle. 0.45 × (W_wide + W_narrow) × L × depth approximates the cross-sectional area to within ~5% for typical residential kidney pools. The Pool Nerd and Pentair both publish this coefficient; we match.

Garden hose GPM at 40 PSI reflects ½″ ≈ 5 gpm, 5/8″ ≈ 9 gpm, ¾″ ≈ 17 gpm — published manufacturer data sheets (Plastic Pipe & Fittings Association). Pressure variance (residential supply ranges 40-80 PSI typically) and hose-length friction loss can shift these ±20%.

Sump pump GPM comes from published pump curves at typical residential head (~10 ft): Zoeller M53 (1/3 HP) ≈ 30 gpm, M63 (1/2 HP) ≈ 50 gpm, Liberty 257 (3/4 HP) ≈ 70 gpm. Curves drop as head rises; for a pool with 20+ ft of hose vertical run + length friction, derate ~15-25% from the published number.

Water cost default $5 / 1,000 gal is the 2024 US urban combined water + sewer average from the Circle of Blue Annual US Water Rate Survey. Check your municipal utility bill — many markets are 50% above or below this default.

Chemical doses follow standard pool operator references (NSPF / PHTA Pool Operator Handbook, Taylor Technologies Pool Chemistry Reference): 1 oz of 12.5% sodium hypochlorite per 1,000 gallons raises Free Chlorine 1 ppm; ~4 lb CYA stabilizer per 10,000 gal brings baseline to ~30 ppm; and salt for residential salt-chlorinator cells targets 3,200 ppm at 8.345 × 10⁻⁶ lb per gallon per ppm raise.

Every fixture in sites/diy/src/data/tools/pool-gallon-calculator/fixtures.json runs in CI before each deploy. If the math drifts, the build fails.

Three real-world examples

Suburban 32×16 rectangle with 3-8 ft slope

The most common American backyard pool. 32 ft × 16 ft with a shallow end at 3 ft and deep end at 8 ft. Average depth: 5.5 ft. Volume = 32 × 16 × 5.5 × 7.4805 ≈ 21,050 gallons (79,700 L). At a 5/8″ garden hose pulling ~9 gpm, full fill takes 39 hours — start Friday morning, swim Sunday afternoon. At $5 per 1,000 gal, refill cost ≈ $105. For winter close-down with a 1/2 HP sump pump (50 gpm), drain time is ~7 hours — an afternoon. Start-up chemicals: ~63 oz liquid chlorine, ~8.4 lb CYA stabilizer, and ~560 lb salt if it's a salt-chlorinator pool.

18-ft round Intex above-ground at 4 ft uniform depth

Most popular above-ground SKU. 18-ft diameter × 4 ft uniform depth: volume = π × 9² × 4 × 7.4805 ≈ 7,600 gallons. At 5/8″ hose: ~14 hours fill. At $5/1k gal: ~$38 refill. A 1/3 HP sump pump drains it in ~4 hours (no need for the bigger pump — small pools don't justify the upgrade). Start-up chemicals: ~23 oz liquid chlorine, ~3 lb CYA, ~205 lb salt. For an above-ground without a salt cell, ignore the salt number.

Kidney pool: 30 ft long, 15-ft wide / 8-ft narrow, slope 3-7 ft

Common residential kidney shape — bigger end is the swim-out / shallow lounger; narrower end is the deep end. Volume = 0.45 × (15+8) × 30 × 5 × 7.4805 ≈ 11,600 gallons. At 5/8″ hose: ~22 hours fill. At $5/1k: ~$58. 1/2 HP pump: ~4 hours drain. Chemicals: ~35 oz liquid chlorine, ~4.6 lb CYA, ~310 lb salt. A modest 11K-gallon pool is right at the bag-chemical / mid-tier maintenance breakpoint — bulk pool-supply purchases pay for themselves about a year in.

What affects how accurate this is

The math is exact; the inputs are approximate. A pool's actual volume can vary 5-15% from the calculator output depending on:

• The pool's volume tag. Most in-ground pools have a plaque or sticker (usually on the equipment pad) with the manufacturer's measured volume. That's the authoritative number — use it before the calculator if you have it.
• Slope geometry. The calculator assumes a constant slope from shallow to deep. Real pools often have a "shelf" at the shallow end and a sharper transition zone — true average depth can be 6-12% off from the (shallow + deep) / 2 simple average. For pools with prominent shelves or stepped depth zones, treat the calculator output as ±10%.
• Spa attachment. Many in-ground pools have an attached spa with shared circulation. The spa adds ~250-500 gallons. Treat as separate.
• Coping rim and skimmer setpoint. The calculator assumes water level at the top edge. Actual operating level is typically 4-6″ below the rim (at the skimmer midline). For a 32×16 pool that's ~450 gallons less than the calculator number.
• Tile shelf / sun shelf / Baja shelf. Many modern pools have a 12-18″ deep tanning ledge spanning 8-15 ft. The calculator's "shallow end" input should be the deeper portion of the pool, not the shelf — the shelf area is small enough that ignoring it is fine for chemistry but matters for surface-area calculations.
• Local hose pressure. The fill-time numbers assume 40 PSI city water. Well water + booster pump might run 55-60 PSI (faster); rural / hilltop properties might be 30 PSI (slower). Hose length matters too — every 50 ft of ½″ hose adds ~5-10% friction loss.
• Pump head and discharge length. Sump pump GPM ratings are published at a single point on the curve (typically 10 ft of head). For a pool with 20 ft of vertical lift + 50 ft of discharge run, derate ~20-30% from the rated GPM — your real drain time will be longer than the calculator shows.

For the tools that actually do the work — draining the pool, filtering the fill water, cleaning around the deck — see Jake's writeups on sump pumps (the 1/2 HP submersibles are what most pool owners need for a full drain-down), whole-house water filters (filter the fill water before it goes in — saves chemistry headaches later), shop vacs for deck and cover cleanup, and pressure washers for spring open-up resurfacing of vinyl backing and concrete coping.

Frequently asked questions

How do you calculate gallons of a pool?

Multiply length × width × average depth (in feet) × 7.4805 for a rectangular pool. For non-rectangular shapes, swap the area formula: π × radius² for round, π/4 × L × W for oval, 0.45 × (wide + narrow widths) × L for kidney. Average depth for a sloped pool is (shallow + deep) / 2. This calculator does all six shape variations automatically — pick the shape, enter dimensions, the math runs in real time.

How many gallons is a 32×16 pool?

Depends on average depth. At 3.5 ft average (no slope, above-ground style): ~13,400 gallons. At 5.5 ft average (typical in-ground slope from 3 ft to 8 ft): ~21,050 gallons. At 6 ft average (deeper diving pool): ~23,000 gallons. The shape and dimensions are constant; the depth profile is what shifts the number 50%+. Enter your real shallow + deep ends in the calculator above for an exact figure.

How big is a 10,000 gallon pool?

Several configurations hit ~10,000 gallons. A 14 × 28 ft rectangle at 3.5 ft average is ~10,300 gal. A 21-ft round above-ground at 4 ft uniform depth is ~10,300 gal. A 16 × 32 ft rectangle at 2.5 ft average (kiddie depth) is ~9,600 gal. Most "small-in-ground" pools land in the 8,000–14,000 gal range; most above-ground rounds 18–24 ft diameter land 7,000–14,000 gal. Enter your dimensions to get an exact figure.

How do I calculate a kidney-shaped pool?

Use 0.45 × (W_wide + W_narrow) × L × avg_depth × 7.4805. W_wide is the wider end's width; W_narrow is the narrower end's width; L is the length end-to-end. The 0.45 coefficient is the residential pool-industry standard approximation for kidney area — the actual shape is between an ellipse and a rectangle, and 0.45 brings the area within ~5% of the true value for typical residential kidney pools. Enter the three measurements in the kidney mode above; this calculator does the rest.

Can I embed this calculator on my site?

Yes — copy the iframe snippet at the bottom of this page. The embedded version is a stripped-down variant designed for /r/pools, /r/swimmingpools, /r/HomeImprovement, pool-service / pool-cleaning blogs, sump-pump retailer blogs, and pool-supply sites. Required attribution is built in. Free, no signup, no analytics attached to the embed.

Related tools

• Sonotube Calculator — full concrete-pour BOM for Sonotube footings (deck posts, pole-barn columns, pergola anchors next to the pool)
• Retaining Wall Calculator — segmental block, base aggregate, drainage stone, and adhesive BOM for the wall around your pool patio
• Sod Calculator — sod, pallet, and delivery-weight estimator for the lawn around your pool deck
• Brick Calculator — multi-wall brick and mortar BOM for masonry coping, pool-house walls, or hardscape
• Browse all free tools by Jake →

Recommended tools for pool work

Pool ownership has a tool list that overlaps with general DIY but isn't identical. Beyond the pool kit itself, here's what's on every Morrison-Construction pool-owner's recommended-equipment list:

• Best Sump Pumps — the most useful single tool a pool owner can own. 1/2 HP submersible drains a typical 15K-gal pool in ~5 hours for winter close-down, repairs, or full water replacement.
• Best Whole-House Water Filters — filter the fill water before it goes in. Removes sediment, iron, and chlorine off-gassing variability that otherwise chases your chemistry for weeks.
• Best Shop Vacs — wet/dry around the pool deck. Leaves, spills, cover muck, and winter puddles all live there. A 12-gallon shop vac handles routine deck cleanup; a 16-gallon handles cover-pumping.
• Best Pressure Washers — spring open-up resurfacing of vinyl liner backing, concrete coping, deck stone, and pool-house siding. Electric handles most jobs; gas if you're doing the whole deck.
• Best Cordless Leaf Blowers — fall close-down deck cleanup before the cover goes on. Faster than a broom, less invasive than a pressure wash for routine maintenance.
• Essential Tools for New Homeowners — the 12-tool starter kit Jake recommends, including the wet/dry vac, drill, and impact driver that get used during every pool-equipment swap or repair.

Sources & methodology

• NIST — General Tables of Units of Measurement — 1 cu ft = 7.4805 US gallons = 28.3168 L conversion.
• NSPF / PHTA Pool Operator Handbook — liquid chlorine (12.5% sodium hypochlorite) dose of 1 oz per 1,000 gal raises Free Chlorine ~1 ppm. Industry standard pool operator certification reference.
• Taylor Technologies — Pool Water Chemistry Reference — CYA stabilizer target 30-50 ppm for outdoor pools; ~4 lb per 10,000 gal raises CYA ~30 ppm baseline.
• Hayward / Pentair / Jandy — Residential salt chlorinator specs — 3,200 ppm NaCl target standard; SWG salt conversion 8.345 × 10⁻⁶ lb / gallon / ppm.
• Plastic Pipe & Fittings Association — garden hose flow rates at 40 PSI: ½″ ≈ 5 gpm, 5/8″ ≈ 9 gpm, ¾″ ≈ 17 gpm.
• Zoeller / Wayne / Liberty pump curves — 1/3 HP submersible ≈ 30 gpm, 1/2 HP ≈ 50 gpm, 3/4 HP ≈ 70 gpm at typical residential 10 ft head.
• Circle of Blue — 2024 Annual US Water Rate Survey — $5 / 1,000 gal combined water + sewer urban average.
• The Pool Nerd — Industry shape coefficient reference — kidney coefficient 0.45, oval ellipse formula π/4 × L × W.

This calculator is reviewed annually for source currency. About Jake · Last reviewed May 28, 2026.

Embed this tool on your site

Free for /r/pools, /r/swimmingpools, /r/HomeImprovement, pool-service and pool-cleaning blogs, sump-pump retailer blogs, pool-supply sites, and hardscape contractor sites. Required attribution is included in the snippet. No fee, no account, no analytics attached to the embed.

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