Water Pressure Drop Calculator
ANA›Life Services Authority›National Calculator Authority›Water Pressure Drop 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; } }
Water Pressure Drop Calculator
Calculate pressure drop in water pipes using the Darcy-Weisbach equation combined with the Colebrook-White friction factor for turbulent flow.
Pipe Length (m)
Pipe Inner Diameter (mm)
Flow Rate (L/min)
Pipe Roughness (mm)
Steel≈0.046, Copper≈0.0015, PVC≈0.0015, Cast Iron≈0.26
Water Temperature (°C)
Calculate Pressure Drop
Enter values above and click Calculate.
function watCalc() { const resultDiv = document.getElementById('wat-result');
const L = parseFloat(document.getElementById('wat-length').value); const Dmm = parseFloat(document.getElementById('wat-diameter').value); const Qlpm = parseFloat(document.getElementById('wat-flowrate').value); const eMm = parseFloat(document.getElementById('wat-roughness').value); const T = parseFloat(document.getElementById('wat-temp').value);
// --- Input validation --- if (isNaN(L) || L Pipe length must be a positive number.'; return; } if (isNaN(Dmm) || Dmm Pipe diameter must be a positive number.'; return; } if (isNaN(Qlpm) || Qlpm Flow rate must be a positive number.'; return; } if (isNaN(eMm) || eMm Roughness must be zero or positive.'; return; } if (isNaN(T) || T = 100) { resultDiv.innerHTML = 'Temperature must be between 0.1 and 99 °C.'; return; }
// --- Unit conversions --- const D = Dmm / 1000; // m const e = eMm / 1000; // m const Q = Qlpm / 60000; // m³/s
// --- Water density (kg/m³) — empirical fit valid 0–100 °C --- const rho = 999.842 - 0.0622 * T - 0.003821 * T * T + 0.000004 * T * T * T;
// --- Dynamic viscosity (Pa·s) — Vogel equation --- const mu = 2.414e-5 * Math.pow(10, 247.8 / (T + 273.15 - 140));
// --- Kinematic viscosity --- const nu = mu / rho;
// --- Cross-sectional area and velocity --- const A = Math.PI * D * D / 4; const V = Q / A;
// --- Reynolds number --- const Re = V * D / nu;
// --- Friction factor via Colebrook-White (iterative) --- // 1/√f = -2 log10(ε/(3.7D) + 2.51/(Re√f)) // Use Swamee-Jain as initial guess, then iterate let f; if (Re 3.0) velWarning = '⚠️ Velocity exceeds 3 m/s — consider a larger pipe to reduce erosion and noise.
'; if (V Pressure Drop${dP_kPa.toFixed(3)} kPa ${dP_bar.toFixed(4)} bar | ${dP_psi.toFixed(3)} psi | ${dP_mH2O.toFixed(3)} m H₂O Flow Velocity${V.toFixed(3)} m/s Reynolds Number${Re.toFixed(0)} ${regime} Darcy Friction Factor (f)${f.toFixed(6)} Water Density${rho.toFixed(2)} kg/m³ Dynamic Viscosity${(mu * 1000).toFixed(4)} mPa·s Relative Roughness (ε/D)${(e/D).toExponential(4)}
${velWarning} `; }
#### Formulas Used
Darcy-Weisbach Equation:
ΔP = f · (L / D) · (ρ · V² / 2)
Flow Velocity: V = Q / A = Q / (π D² / 4)
Reynolds Number: Re = V · D / ν (ν = μ / ρ)
Friction Factor:
- Turbulent (Re ≥ 4000): Colebrook-White equation (iterated to convergence): 1/√f = −2 log₁₀( ε/(3.7D) + 2.51/(Re √f) )
Water Density (empirical, 0–100 °C): ρ = 999.842 − 0.0622T − 0.003821T² + 4×10⁻⁶T³ (kg/m³)
Dynamic Viscosity (Vogel equation): μ = 2.414×10⁻⁵ × 10^(247.8 / (T + 133.15)) (Pa·s)
#### Assumptions & References
- Colebrook-White equation: Colebrook, C.F. (1939), J. Inst. Civil Engineers, 11, 133–156.
- Darcy-Weisbach: Moody, L.F. (1944), Trans. ASME, 66(8), 671–684.
- Viscosity: Vogel, H. (1921), Physikalische Zeitschrift, 22, 645–646.
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