Well Pump Horsepower & Flow Rate Calculator
ANA›Life Services Authority›National Calculator Authority›Well Pump Horsepower & Flow Rate 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 Horsepower & Flow Rate Calculator
Calculate the required brake horsepower (BHP) for a well pump given flow rate and total dynamic head, or determine the flow rate from a known horsepower. Uses the standard hydraulic horsepower formula with pump and motor efficiency factors.
Calculation Mode
Calculate Horsepower from Flow Rate Calculate Flow Rate from Horsepower
Flow Rate (GPM)
Gallons per minute delivered by the pump
Motor Horsepower (HP)
Rated horsepower of the motor driving the pump
Total Dynamic Head (ft)
Sum of static head + friction losses + pressure head (feet of water)
Pump Efficiency (%)
Typical submersible well pumps: 50–80%
Motor Efficiency (%)
Typical submersible motors: 85–95%
Fluid Specific Gravity
1.0 for fresh water; use 1.025 for seawater
Calculate
function welToggleMode() { var mode = document.getElementById('wel_calc_mode').value; document.getElementById('wel_flow_input').style.display = (mode === 'hp') ? '' : 'none'; document.getElementById('wel_hp_input').style.display = (mode === 'flow') ? '' : 'none'; document.getElementById('wel_result').style.display = 'none'; }
function welCalc() { var resultDiv = document.getElementById('wel_result'); resultDiv.style.display = 'none';
var mode = document.getElementById('wel_calc_mode').value; var tdh = parseFloat(document.getElementById('wel_total_head').value); var pumpEff = parseFloat(document.getElementById('wel_pump_eff').value); var motorEff = parseFloat(document.getElementById('wel_motor_eff').value); var sg = parseFloat(document.getElementById('wel_fluid_sg').value);
// --- Validation --- var errors = [];
if (isNaN(tdh) || tdh = 100) errors.push('Pump Efficiency must be between 1 and 99%.'); if (isNaN(motorEff) || motorEff = 100) errors.push('Motor Efficiency must be between 1 and 99%.'); if (isNaN(sg) || sg 3.0) errors.push('Specific Gravity must be between 0.5 and 3.0.');
var flow = NaN, motorHp = NaN;
if (mode === 'hp') { flow = parseFloat(document.getElementById('wel_flow_rate').value); if (isNaN(flow) || flow 0) { resultDiv.innerHTML = 'Please fix the following:' + errors.map(function(e){ return ''; }).join('') + ''; resultDiv.style.display = 'block'; return; }
// --- Formulas --- // Hydraulic HP (WHP) = (GPM × TDH × SG) / 3960 // Brake HP (BHP) = WHP / pump_efficiency // Motor HP (MHP) = BHP / motor_efficiency // Rearranged for flow: GPM = (MHP × pump_eff × motor_eff × 3960) / (TDH × SG)
var pumpEffDec = pumpEff / 100.0; var motorEffDec = motorEff / 100.0; var overallEff = pumpEffDec * motorEffDec;
var whp, bhp, mhp, gpm;
if (mode === 'hp') { gpm = flow; whp = (gpm * tdh * sg) / 3960.0; bhp = whp / pumpEffDec; mhp = bhp / motorEffDec; } else { mhp = motorHp; bhp = mhp * motorEffDec; whp = bhp * pumpEffDec; gpm = (whp * 3960.0) / (tdh * sg); }
// Wire-to-water efficiency var wireToWater = (whp / mhp) * 100.0;
// Suggested standard motor size (next standard size up) var stdSizes = [0.5, 0.75, 1.0, 1.5, 2.0, 3.0, 5.0, 7.5, 10.0, 15.0, 20.0, 25.0, 30.0, 40.0, 50.0, 75.0, 100.0]; var suggestedMotor = null; for (var i = 0; i = mhp) { suggestedMotor = stdSizes[i]; break; } } if (suggestedMotor === null) suggestedMotor = '> 100 (custom)';
// Flow velocity context (rough: 1 GPM ≈ 0.00223 ft³/s) var gph = gpm * 60.0; var gpd = gpm * 1440.0;
// --- Output --- var html = '### Results ';
if (mode === 'hp') { html += 'ParameterValue'; html += 'Flow Rate' + gpm.toFixed(2) + ' GPM'; html += 'Water Horsepower (WHP)' + whp.toFixed(4) + ' HP'; html += 'Brake Horsepower (BHP)' + bhp.toFixed(4) + ' HP'; html += 'Required Motor HP (MHP)' + mhp.toFixed(4) + ' HP'; html += 'Suggested Standard Motor Size' + suggestedMotor + ' HP'; } else { html += 'ParameterValue'; html += 'Motor Horsepower (MHP)' + mhp.toFixed(4) + ' HP'; html += 'Brake Horsepower (BHP)' + bhp.toFixed(4) + ' HP'; html += 'Water Horsepower (WHP)' + whp.toFixed(4) + ' HP'; html += 'Achievable Flow Rate' + gpm.toFixed(2) + ' GPM'; }
html += 'Total Dynamic Head' + tdh.toFixed(1) + ' ft'; html += 'Pump Efficiency' + pumpEff.toFixed(1) + '%'; html += 'Motor Efficiency' + motorEff.toFixed(1) + '%'; html += 'Overall (Wire-to-Water) Efficiency' + wireToWater.toFixed(2) + '%'; html += 'Fluid Specific Gravity' + sg.toFixed(3) + ''; html += 'Flow Rate (GPH)' + gph.toFixed(1) + ' GPH'; html += 'Flow Rate (GPD)' + gpd.toFixed(0) + ' GPD'; html += '';
// Warnings var warnings = []; if (wireToWater 1000) warnings.push('Total Dynamic Head exceeds 1,000 ft — verify this is correct for your application.'); if (gpm 100) warnings.push('Required motor HP exceeds 100 HP — this is a large industrial installation.');
if (warnings.length > 0) { html += '⚠ Warnings:' + warnings.map(function(w){ return ''; }).join('') + ''; }
resultDiv.innerHTML = html; resultDiv.style.display = 'block'; }
#### Formulas Used
Water Horsepower (WHP) — the theoretical power needed to move water:
WHP = (GPM × TDH × SG) / 3960
Where 3960 is a unit-conversion constant (derived from 1 HP = 550 ft·lbf/s and 1 gallon of water = 8.34 lb).
Brake Horsepower (BHP) — shaft power required at the pump, accounting for pump losses:
BHP = WHP / ηpump
Motor Horsepower (MHP) — electrical input power required, accounting for motor losses:
MHP = BHP / ηmotor = (GPM × TDH × SG) / (3960 × ηpump × ηmotor)
Rearranged for Flow Rate:
GPM = (MHP × ηpump × ηmotor × 3960) / (TDH × SG)
Wire-to-Water Efficiency:
ηw2w = WHP / MHP = ηpump × ηmotor
Total Dynamic Head (TDH) components:
TDH = Static Lift + Friction Head Loss + Pressure Head + Velocity Head
#### Assumptions & References
- The constant 3960 is derived from: 1 HP = 550 ft·lbf/s; water density = 8.34 lb/gal; 1 gal/min = 1/60 gal/s → 3960 = (33,000 ft·lbf/min) / 8.34 lb/gal.
- Specific gravity of 1.0 is assumed for fresh water at standard conditions (60°F / 15.6°C).
- Typical submersible well pump efficiencies range from 50–80%; centrifugal pumps 60–85%.
- Typical submersible motor efficiencies range from 85–95%.
- This calculator does not account for NPSH (Net Positive Suction Head) — verify separately for surface pumps.
- References: Goulds Pumps Engineering Data Book; Grundfos Pump Handbook; AWWA M21 Groundwater; Hydraulic Institute Standards.
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