Well Pump Pressure Tank Size Calculator

ANA›Life Services Authority›National Calculator Authority›Well Pump Pressure Tank Size Calculator

.calc-container { max-width: 640px; margin: 2rem 0; padding: 1.5rem; background: #fff; border: 1px solid #ddd; border-radius: 8px; box-shadow: 0 1px 3px rgba(0,0,0,0.06); font-family: system-ui, -apple-system, sans-serif; } .calc-container h3 { font-family: Georgia, serif; font-size: 1.15rem; color: #1a1a1a; margin-bottom: 1rem; padding-bottom: 0.5rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-row { display: flex; align-items: center; gap: 0.75rem; margin-bottom: 0.75rem; flex-wrap: wrap; } .calc-row label { min-width: 160px; font-size: 0.9rem; color: #333; font-weight: 500; } .calc-row input[type="number"], .calc-row select { flex: 1; min-width: 120px; max-width: 200px; padding: 0.5rem 0.6rem; border: 1px solid #ccc; border-radius: 4px; font-size: 0.9rem; font-family: system-ui, sans-serif; color: #1a1a1a; background: #fafaf8; } .calc-row input:focus, .calc-row select:focus { outline: none; border-color: var(--ac, #3d5a80); box-shadow: 0 0 0 2px rgba(26,74,138,0.12); } .calc-row .unit { font-size: 0.82rem; color: #888; min-width: 30px; } .calc-btn { display: inline-block; margin-top: 0.5rem; padding: 0.55rem 1.5rem; background: var(--ac, #3d5a80); color: #fff; border: none; border-radius: 4px; font-size: 0.9rem; font-weight: 600; cursor: pointer; font-family: system-ui, sans-serif; } .calc-btn:hover { opacity: 0.9; } .calc-result { margin-top: 1.25rem; padding: 1rem 1.25rem; background: #f0f6fc; border-left: 3px solid var(--ac, #3d5a80); border-radius: 0 6px 6px 0; display: none; } .calc-result.visible { display: block; } .calc-result-label { font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.06em; color: #666; margin-bottom: 0.25rem; } .calc-result-value { font-size: 1.6rem; font-weight: 700; color: var(--ac, #3d5a80); } .calc-result-detail { font-size: 0.85rem; color: #555; margin-top: 0.5rem; line-height: 1.5; } .calc-note { margin-top: 1rem; font-size: 0.8rem; color: #888; font-style: italic; } .calc-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0.75rem; margin-top: 0.75rem; } .calc-grid-item { padding: 0.6rem 0.8rem; background: #f8f9fa; border-radius: 4px; border: 1px solid #eee; } .calc-grid-item .label { font-size: 0.75rem; color: #888; text-transform: uppercase; letter-spacing: 0.04em; } .calc-grid-item .value { font-size: 1.1rem; font-weight: 600; color: #1a1a1a; } @media (max-width: 720px) { .calc-row { flex-direction: column; align-items: flex-start; gap: 0.3rem; } .calc-row label { min-width: auto; } .calc-row input[type="number"], .calc-row select { max-width: 100%; width: 100%; } .calc-grid { grid-template-columns: 1fr; } } .calc-chart { margin: 1rem 0; text-align: center; } .calc-chart svg { max-width: 100%; height: auto; } .calc-chart-legend { display: flex; flex-wrap: wrap; justify-content: center; gap: 0.6rem 1.2rem; margin-top: 0.6rem; font-size: 0.8rem; color: #555; } .calc-chart-legend span { display: inline-flex; align-items: center; gap: 0.3rem; } .calc-chart-legend i { display: inline-block; width: 10px; height: 10px; border-radius: 2px; font-style: normal; } .calc-related { max-width: 640px; margin: 2rem 0 1rem; padding: 1.25rem 1.5rem; background: #f8f9fa; border: 1px solid #e8e8e8; border-radius: 8px; } .calc-related h3 { font-family: Georgia, serif; font-size: 1rem; color: #1a1a1a; margin: 0 0 0.75rem; padding-bottom: 0.4rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-related-list { list-style: none; padding: 0; margin: 0 0 0.75rem; display: grid; grid-template-columns: 1fr 1fr; gap: 0.4rem 1.5rem; } .calc-related-list li a { font-size: 0.88rem; color: var(--ac, #3d5a80); text-decoration: none; } .calc-related-list li a:hover { text-decoration: underline; } .calc-browse-all { margin: 0.5rem 0 0; font-size: 0.9rem; font-weight: 600; } .calc-browse-all a { color: var(--ac, #3d5a80); text-decoration: none; } .calc-browse-all a:hover { text-decoration: underline; } @media (max-width: 720px) { .calc-related-list { grid-template-columns: 1fr; } }

Well Pump Pressure Tank Size Calculator

Calculate the minimum pressure tank size needed for your well pump system to prevent short cycling and extend pump life.

Pump Flow Rate (GPM)

Gallons per minute rating of your well pump

Cut-In Pressure (PSI)

Pressure at which the pump turns ON (commonly 30 or 40 PSI)

Cut-Out Pressure (PSI)

Pressure at which the pump turns OFF (commonly 50 or 60 PSI)

Maximum Pump Cycles per Hour

Recommended: 6 cycles/hr for most pumps (check manufacturer specs)

Tank Pre-Charge Pressure (PSI)

Air pre-charge pressure (typically 2 PSI below cut-in pressure)

Calculate Tank Size

function welCalc() { var resultDiv = document.getElementById('wel-result');

var Q = parseFloat(document.getElementById('wel-flow-rate').value); var Pc = parseFloat(document.getElementById('wel-cut-in').value); var Po = parseFloat(document.getElementById('wel-cut-out').value); var N = parseFloat(document.getElementById('wel-cycles').value); var Pp = parseFloat(document.getElementById('wel-precharge').value);

// --- Validation --- if (isNaN(Q) || isNaN(Pc) || isNaN(Po) || isNaN(N) || isNaN(Pp)) { resultDiv.innerHTML = 'Please fill in all fields.

'; return; } if (Q = Pc) { resultDiv.innerHTML = 'Pre-charge pressure must be less than cut-in pressure (recommended: 2 PSI below cut-in).

'; return; }

// --- Convert PSI to absolute pressure (PSIA) --- // Absolute pressure = gauge pressure + 14.7 (atmospheric) var Pc_abs = Pc + 14.7; var Po_abs = Po + 14.7; var Pp_abs = Pp + 14.7;

// --- Drawdown Volume (gallons) --- // Drawdown = Q / (N * 4) [standard formula: Vd = Q / (4 * N)] // This is the usable water volume the tank must hold per cycle var Vd = Q / (4 * N);

// --- Total Tank Volume (gallons) using Boyle's Law acceptance ratio --- // Acceptance ratio: Ar = 1 - (Pc_abs / Po_abs) // But with pre-charge considered: // Ar = (Pp_abs / Pc_abs) * (1 - Pc_abs / Po_abs) // Total Tank Volume: Vt = Vd / Ar var Ar = (Pp_abs / Pc_abs) * (1 - (Pc_abs / Po_abs));

if (Ar = Vt_recommended) { suggestedSize = commonSizes[i]; break; } } if (!suggestedSize) suggestedSize = "> 220 (custom tank required)";

// --- Cycle time --- var runTime = (Vd / Q) * 60; // seconds pump runs per cycle var totalTime = 3600 / N; // seconds per cycle var offTime = totalTime - runTime;

resultDiv.innerHTML = '### Results ' + '' + 'ParameterValue' + 'Drawdown Volume Required' + Vd.toFixed(2) + ' gallons' + 'Acceptance Ratio' + (Ar * 100).toFixed(1) + '%' + 'Minimum Tank Size (calculated)' + Vt.toFixed(1) + ' gallons' + 'Recommended Tank Size (+25% margin)' + Vt_recommended.toFixed(1) + ' gallons' + 'Nearest Standard Tank Size' + suggestedSize + ' gallons' + 'Pump Run Time per Cycle' + runTime.toFixed(1) + ' seconds' + 'Pump Off Time per Cycle' + offTime.toFixed(1) + ' seconds' + '' + 'Pre-charge the tank to ' + Pp + ' PSI (with no water in tank) before installation.

'; }

#### Formulas Used

1. Drawdown Volume (Vd):

Vd = Q ÷ (4 × N)

2. Acceptance Ratio (Ar) — using Boyle's Law:

Ar = (Ppre / Pcut-in) × (1 − Pcut-in / Pcut-out)

All pressures converted to absolute (PSIA) by adding 14.7 PSI atmospheric pressure.

3. Minimum Tank Volume (Vt):

Vt = Vd ÷ Ar

4. Recommended Tank Volume:

Vrecommended = Vt × 1.25 (25% safety margin)

#### Assumptions & References

More Calculators

Read Next

Study Time Planner ANA › Life Services Authority › National Calculator Authority › Study Time Planner .calc-container { max-width: 640px; margin:...

References

Related Authorities

Life Services Authority › Professional Services Authority › Trade Services Authority › United States Authority ›