Airflow CFM Calculator
ANA›Life Services Authority›National Calculator Authority›Airflow CFM 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; } }
Airflow CFM Calculator
Calculate airflow in cubic feet per minute (CFM) using either the Velocity Method (duct velocity × area) or the Air Changes Per Hour (ACH) Method (room volume ÷ 60 × ACH).
Calculation Method:
Velocity Method
ACH Method
Air Velocity (FPM — feet per minute):
Duct Shape:
Rectangular Circular (Round)
Duct Width (inches):
Duct Height (inches):
Duct Diameter (inches):
Room Length (feet):
Room Width (feet):
Ceiling Height (feet):
Air Changes Per Hour (ACH):
Typical: Residential 4–6, Office 6–10, Hospital 15–20, Clean Room 20–60
Calculate CFM
#### Formulas Used
Velocity Method:
CFM = Velocity (FPM) × Area (ft²)
Rectangular duct area: A = (Width × Height) / 144 (converts in² → ft²)
Circular duct area: A = π × (Diameter / 2)² / 144 (converts in² → ft²)
ACH Method:
CFM = (Room Volume (ft³) × ACH) / 60
Room Volume: V = Length × Width × Height
#### Assumptions & References
- The ACH Method divides by 60 to convert air changes per hour into per minute (CFM).
function airToggleMethod() { var method = document.querySelector('input[name="air-method"]:checked').value; document.getElementById('air-velocity-inputs').style.display = (method === 'velocity') ? 'block' : 'none'; document.getElementById('air-ach-inputs').style.display = (method === 'ach') ? 'block' : 'none'; document.getElementById('air-result').innerHTML = ''; }
function airToggleDuctShape() { var shape = document.getElementById('air-shape').value; document.getElementById('air-rect-inputs').style.display = (shape === 'rectangular') ? 'block' : 'none'; document.getElementById('air-circ-inputs').style.display = (shape === 'circular') ? 'block' : 'none'; document.getElementById('air-result').innerHTML = ''; }
function airCalc() { var resultDiv = document.getElementById('air-result'); var method = document.querySelector('input[name="air-method"]:checked').value;
if (method === 'velocity') { var velocity = parseFloat(document.getElementById('air-velocity').value); var shape = document.getElementById('air-shape').value;
if (isNaN(velocity) || velocity ⚠ Please enter a valid air velocity greater than 0 FPM.'; return; }
var areaSqFt;
if (shape === 'rectangular') { var w = parseFloat(document.getElementById('air-width').value); var h = parseFloat(document.getElementById('air-height').value); if (isNaN(w) || w ⚠ Please enter valid duct width and height greater than 0 inches.'; return; } areaSqFt = (w * h) / 144; var cfm = velocity * areaSqFt; resultDiv.innerHTML = 'Results (Velocity Method — Rectangular Duct):' + 'Duct Width: ' + w.toFixed(2) + ' in' + 'Duct Height: ' + h.toFixed(2) + ' in' + 'Duct Area: ' + areaSqFt.toFixed(4) + ' ft² (' + (w * h).toFixed(2) + ' in²)' + 'Air Velocity: ' + velocity.toFixed(0) + ' FPM' + '✓ Airflow = ' + cfm.toFixed(1) + ' CFM';
} else { var d = parseFloat(document.getElementById('air-diameter').value); if (isNaN(d) || d ⚠ Please enter a valid duct diameter greater than 0 inches.'; return; } areaSqFt = Math.PI * Math.pow(d / 2, 2) / 144; var cfm = velocity * areaSqFt; resultDiv.innerHTML = 'Results (Velocity Method — Circular Duct):' + 'Duct Diameter: ' + d.toFixed(2) + ' in' + 'Duct Area: ' + areaSqFt.toFixed(4) + ' ft² (' + (Math.PI * Math.pow(d/2, 2)).toFixed(2) + ' in²)' + 'Air Velocity: ' + velocity.toFixed(0) + ' FPM' + '✓ Airflow = ' + cfm.toFixed(1) + ' CFM'; }
} else { // ACH Method var rLen = parseFloat(document.getElementById('air-room-length').value); var rWid = parseFloat(document.getElementById('air-room-width').value); var rHgt = parseFloat(document.getElementById('air-room-height').value); var ach = parseFloat(document.getElementById('air-ach').value);
if (isNaN(rLen) || rLen ⚠ Please enter a valid room length greater than 0 ft.'; return; } if (isNaN(rWid) || rWid ⚠ Please enter a valid room width greater than 0 ft.'; return; } if (isNaN(rHgt) || rHgt ⚠ Please enter a valid ceiling height greater than 0 ft.'; return; } if (isNaN(ach) || ach ⚠ Please enter a valid ACH value greater than 0.'; return; }
var volume = rLen * rWid * rHgt; var cfm = (volume * ach) / 60;
resultDiv.innerHTML = 'Results (ACH Method):' + 'Room Dimensions: ' + rLen.toFixed(1) + ' ft × ' + rWid.toFixed(1) + ' ft × ' + rHgt.toFixed(1) + ' ft' + 'Room Volume: ' + volume.toFixed(1) + ' ft³' + 'Air Changes Per Hour: ' + ach.toFixed(1) + ' ACH' + '✓ Required Airflow = ' + cfm.toFixed(1) + ' CFM' + '(' + volume.toFixed(1) + ' ft³ × ' + ach.toFixed(1) + ' ACH ÷ 60 min/hr = ' + cfm.toFixed(1) + ' CFM)'; } }
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