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Air Purifier CADR Calculator

Estimate the clean air delivery rate needed for a room from its volume and a chosen target air-change rate.

ft
Enter a number from 1 to 1000.
ft
Enter a number from 1 to 1000.
ft
Enter a number from 1 to 100.
ACH
Enter a number from 0.1 to 20.

Use the units shown. Blanks, words, comma-formatted numbers, fractions, non-finite values and values outside the stated ranges are rejected.

Required CADR
Required CADR
Room volume

How to use this calculator

  1. Replace every example value with your own measurements, label values or planning assumptions.
  2. Keep each value in the unit printed beside its field.
  3. Select Calculate, then compare the result with the formula and limitations below.

Formula and method

Room volume = length × width × ceiling height. Required CADR in cubic feet per minute = room volume × target air changes per hour ÷ 60. Multiply cfm by 1.69901 for m³/hr.

Results are hidden whenever an input changes or validation fails, so an older answer cannot be mistaken for the current calculation.

Worked example

Room length = 20 ft; Room width = 15 ft; Ceiling height = 8 ft; Target air changes = 4 ACH. The calculator returns Required CADR = 160 cfm; Required CADR = 272 m³/hr; Room volume = 2400 cu ft.

The worked example uses the same default values displayed in the calculator.

Limitations and safety

CADR applies to particles and does not guarantee removal of gases or every pollutant. EPA says filtration supplements source control and ventilation; compare pollutant-specific CADR and avoid devices that intentionally generate ozone.

Frequently asked questions

What should I enter first?

Start with measurements or rates from the project, product label, service quote or equipment specification. Replace every example value before relying on the estimate.

Why can the real result differ?

CADR applies to particles and does not guarantee removal of gases or every pollutant. EPA says filtration supplements source control and ventilation; compare pollutant-specific CADR and avoid devices that intentionally generate ozone.

Does the calculator round purchases up?

Only outputs labeled as whole packages, vents, heaters, pails or similar counts are rounded up. Keep extra precision for planning and follow supplier packaging.

Review notes and reference

Reviewed October 5, 2026. The formula was independently checked against the displayed default example, and the calculator was tested for valid defaults, empty input, invalid formats, range boundaries and recovery. Reference: EPA Guide to Air Cleaners in the Home. Explanations and examples are original.

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