Pool Pump Size Calculator

Sizing a pump means matching three coupled numbers. First the required flow: the GPM that turns the whole pool over in your target hours. Then the total dynamic head (TDH) the plumbing imposes at that flow. Then the HP band that delivers that GPM against that head — checked against what your pipe and filter can actually pass.

requiredGpm  = volumeGal / (turnoverHours × 60)

TDH (ft)     = pipeFriction + fittingFriction + staticLift + ~10 ft equipment
  pipeFriction    = friction/100ft × (runFt / 100)
  fittingFriction = elbows × elbowEquivLength × friction/100ft ÷ 100
  staticLift      = inground vs above-ground baseline (decomposed)

pipeCapGpm   = 1.5″ 43 · 2″ 73 · 2.5″ 120
filterCapGpm = filterArea × (sand 20 · cartridge 0.325 · DE 1.75 GPM/ft²)
ceilingGpm   = min(pipe, filter);  over when requiredGpm > ceiling

hpBand       = residential lookup from GPM at TDH  (a band, not a single value)

Friction loss uses the Hazen-Williams relation for Schedule 40 PVC (C = 140), the same basis as published pool-plumbing friction charts; a 90° elbow adds an equivalent ~4–6 ft of pipe depending on size. We add a fixed ~10 ft equipment allowance for the filter and heater, and a pool-type static-lift baseline decomposed so the 10 ft is never double-counted — a default-plumbing in-ground pool lands near the industry ~50 ft reference, above-ground near ~30 ft.

HP is a band, never a single number. The same GPM at the same head can be met by different pumps depending on the individual pump curve and efficiency, so we give a residential band and tell you to verify against the actual pump's flow curve before buying. The most common reason a "correct GPM" is unachievable is a pipe or filter that can't pass it — so we surface that as a visible warning, not fine print. The From dimensions mode borrows the same volume engine as the Pool Volume Calculator (7.48 gal/ft³, primary-source-validated shape constants).

Sources: PoolSizer — Pool Pump Calculator; Pool Research — Pump Size Calculator; Saltwater Pool & Spa — Pool Pump Sizing. PVC friction via Hazen-Williams (C = 140), checked against published Schedule 40 friction charts.