Convert Cfm to Mph Calculator

CFM to MPH Calculator

Convert Airflow Volume to Air Speed Instantly

Cubic Feet per Minute
Inside diameter of the outlet
Calculated Air Velocity
0 MPH
0 ft/min

How to Convert CFM to MPH

Converting Cubic Feet per Minute (CFM) to Miles Per Hour (MPH) is common when evaluating leaf blowers, HVAC systems, or industrial fans. While CFM measures volume (how much air is moving), MPH measures speed (how fast that air is moving). To convert between the two, you must know the cross-sectional area of the opening through which the air passes.

The Physics Formula

Velocity (MPH) = (CFM × 144) / (Area in Sq Inches × 88)

Step-by-Step Calculation Example

Let's say you have a leaf blower rated at 400 CFM with a 3-inch diameter nozzle:

  1. Calculate Area: For a circle, Area = π × (radius)². Radius is 1.5″, so Area = 3.14159 × (1.5 × 1.5) = 7.068 sq inches.
  2. Convert to Feet: There are 144 square inches in a square foot. Area = 7.068 / 144 = 0.049 sq feet.
  3. Find Feet per Minute: Velocity (ft/min) = CFM / Area (sq ft) = 400 / 0.049 = 8,163 ft/min.
  4. Convert to MPH: Since 88 ft/min equals 1 MPH, Divide 8,163 by 88 = 92.76 MPH.

CFM vs. MPH: Which Matters More?

In equipment like leaf blowers, neither number tells the whole story. High MPH allows you to "break loose" heavy, wet debris, while high CFM allows you to move large piles of dry leaves quickly. A perfect balance of both provides the highest "blowing force" (measured in Newtons).

function calculateAirSpeed() { var cfm = parseFloat(document.getElementById('input_cfm').value); var diameter = parseFloat(document.getElementById('input_diameter').value); var resultBox = document.getElementById('result_box'); var mphDisplay = document.getElementById('mph_result'); var ftminDisplay = document.getElementById('ftmin_result'); if (isNaN(cfm) || isNaN(diameter) || diameter <= 0 || cfm < 0) { alert("Please enter valid positive numbers for both CFM and Diameter."); return; } // 1. Calculate Radius var radius = diameter / 2; // 2. Calculate Area in Square Inches (A = πr²) var areaSqIn = Math.PI * Math.pow(radius, 2); // 3. Calculate Area in Square Feet var areaSqFt = areaSqIn / 144; // 4. Calculate Velocity in Feet per Minute var velocityFtMin = cfm / areaSqFt; // 5. Convert ft/min to MPH (1 MPH = 88 ft/min) var mph = velocityFtMin / 88; // Update Display mphDisplay.innerHTML = mph.toFixed(2) + " MPH"; ftminDisplay.innerHTML = velocityFtMin.toLocaleString(undefined, {maximumFractionDigits: 0}) + " ft/min"; resultBox.style.display = "block"; resultBox.scrollIntoView({ behavior: 'smooth', block: 'nearest' }); }

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