Air Purifier Filter Lifespan Calculator

How this air purifier filter lifespan estimate works

This calculator estimates how long an air purifier filter can be used before it is likely to be saturated with particulate pollution. It focuses on fine particulate matter (PM2.5), which is one of the main pollutants targeted by high-efficiency particle filters (such as HEPA). By combining your purifier’s clean air delivery rate (CADR), the surrounding PM2.5 concentration, the filter’s efficiency, its dust-holding capacity, and how many hours per day you run the unit, the calculator produces an approximate operating life for the filter.

The key idea is straightforward:

• Airflow through the filter (CADR) determines how much air is cleaned per hour.
• Pollution concentration (PM2.5) tells us how much particulate mass is in each cubic meter of air.
• Filter efficiency describes what fraction of that particulate mass the filter actually captures.
• Filter capacity describes how many grams of particulate the filter can hold before it is considered “full.”
• Daily operating hours convert the operating life in hours into days and months of real-world use.

By estimating how many grams of particulate the filter collects per hour, and dividing its total capacity by that hourly load, we get a rough lifespan in hours of operation. You can then convert that to calendar days based on how many hours per day you typically run the purifier.

Calculation formula

The calculator uses the following steps to estimate filter life:

1. Convert PM2.5 concentration from micrograms per cubic meter (µg/m³) to grams per cubic meter (g/m³).
2. Multiply by CADR to get grams of particulate entering the filter per hour.
3. Multiply by filter efficiency (as a decimal) to get grams actually captured per hour.
4. Divide the filter’s dust capacity (in grams) by that capture rate to get lifespan in hours of operation.

Let:

• C = filter capacity (g of dust)
• Q = CADR (m³/h)
• PM = PM2.5 concentration (µg/m³)
• E = filter efficiency (fraction, so 99% = 0.99)
• L = filter lifespan (hours of operation)

First, convert PM from micrograms to grams per cubic meter:

Then the hourly particulate mass captured by the filter, M (grams per hour), is:

M = Q × P × E

The filter lifespan in hours of operation is then:

L = C / M = C / (Q × P × E)

Substituting P back in terms of PM in µg/m³ gives:

L = C / (Q × (PM / 1,000,000) × E)

This shows how lifespan changes with each input:

• If you double CADR, you double the amount of polluted air processed per hour, so the filter fills up about twice as fast, and lifespan in hours is roughly cut in half.
• If the PM2.5 concentration doubles, each cubic meter of air contains twice as much particulate, so the filter fills twice as fast and lifespan is roughly halved.
• If the filter capacity doubles, lifespan in hours roughly doubles (holding other factors constant).
• If efficiency increases, the filter captures more particulate per hour, shortening its lifespan in hours. There is a trade-off between clean air and how often you need to replace filters.

What each input means

Clean Air Delivery Rate (CADR)

CADR is the amount of clean air an air purifier can deliver per hour, usually stated in cubic meters per hour (m³/h). You can typically find it on the product box, user manual, or manufacturer’s specification page. Higher CADR means:

• Faster cleaning of a given room or area.
• More air pushed through the filter per hour.
• Faster loading of the filter with particulate.

For many small home purifiers, CADR might range from around 100–400 m³/h. Larger units or units designed for very large rooms will have higher CADR values.

PM2.5 concentration (µg/m³)

PM2.5 consists of airborne particles with diameters less than or equal to 2.5 micrometers. These fine particles can penetrate deep into the lungs and are linked with cardiovascular and respiratory health effects.

You can approximate PM2.5 using:

• Local outdoor air quality data from government or third-party apps.
• Indoor air quality monitors that provide real-time PM2.5 readings.
• Typical ranges for your environment:
  • Clean indoor air: often < 10 µg/m³.
  • Moderately polluted indoor air: ~20–40 µg/m³.
  • Heavily polluted or smoky conditions: 100 µg/m³ and above.

Filter efficiency (%)

Filter efficiency indicates what fraction of PM2.5 the filter removes from the air flowing through it. A high-efficiency filter, such as a true HEPA filter, can reach 99% or more for fine particles. Many manufacturers provide an efficiency rating for specific particle sizes. When entering a value here:

• Use 80–95% for mid-range particulate filters.
• Use 95–99.97% for high-efficiency HEPA filters, depending on the exact specification.
• Remember that higher efficiency usually improves air quality but fills the filter more quickly.

Filter capacity (grams of dust)

Filter capacity is how much particulate mass (dust, smoke particles, etc.) the filter can hold before it should be replaced. Manufacturers may not always state this directly. In that case, you can:

• Consult technical datasheets for the filter model (sometimes listed as “dust holding capacity”).
• Use a rough estimate based on similar filters; many home HEPA cartridges hold on the order of a few tens of grams of fine particulate.
• Run scenarios with a range of capacities (for example, 20 g, 50 g, 80 g) to see how sensitive lifespan is to this assumption.

Hours of operation per day

This is the number of hours you typically run the air purifier each day. The calculator first computes lifespan in hours of operation, then you can convert that to:

• Days of use = lifespan in hours / hours per day.
• Months of use = days of use / ~30.

For example, a filter that lasts 7,200 operating hours will last approximately:

• 300 days at 24 hours per day (continuous operation).
• 600 days at 12 hours per day (intermittent operation).

Interpreting your result

The main output of the calculator is an estimated filter lifespan in hours of active operation, based on your inputs. To make sense of it, consider these steps:

1. Convert hours to days or months using your chosen hours of operation per day.
2. Compare the estimate to the manufacturer’s recommended replacement interval. If the calculator predicts a much shorter interval, your environment may be more polluted than the generic assumptions the manufacturer used. If it predicts a much longer interval, the manufacturer may be using a conservative schedule.
3. Run multiple what-if scenarios:
   • Increase the PM2.5 value to simulate smoke events or high-pollution days.
   • Decrease hours per day to see how intermittent operation affects lifespan.
   • Adjust efficiency to see the trade-off between capture performance and filter replacement frequency.

Remember that the result is an idealized estimate. Real-world filters may be replaced earlier for reasons such as odour buildup, visible dust, or fan noise from a clogged filter, even if their theoretical mass capacity is not fully reached.

Worked example

Consider a purifier with the following characteristics:

• CADR: 200 m³/h
• PM2.5 concentration: 35 µg/m³
• Filter efficiency: 99% (0.99 as a fraction)
• Filter capacity: 50 g of particulate
• Hours of operation per day: 12 hours

Step 1: Convert PM2.5 to grams per cubic meter.

P = 35 µg/m³ ÷ 1,000,000 = 0.000035 g/m³

Step 2: Compute grams entering the filter per hour before efficiency.

Particulate in air per hour = Q × P = 200 × 0.000035 = 0.007 g/h

Step 3: Account for filter efficiency.

Captured mass per hour = 0.007 × 0.99 ≈ 0.00693 g/h

Step 4: Compute lifespan in hours of operation.

L = C / captured mass per hour = 50 / 0.00693 ≈ 7,214 hours

Step 5: Convert to days and months at 12 hours per day.

• Days of use ≈ 7,214 / 12 ≈ 601 days.
• Months of use ≈ 601 / 30 ≈ 20 months.

So under these assumptions, the filter could theoretically last for roughly 20 months when run 12 hours per day in moderately polluted air. In practice, you would likely replace it earlier based on manufacturer guidance or observed performance.

Example scenarios comparison

The table below compares a few simplified scenarios using approximate numbers. In each case, we assume a 50 g filter capacity and 99% efficiency, and we show estimated lifespan at 12 hours per day of operation.

These numbers are illustrative only. They demonstrate how lifespan drops sharply as PM2.5 levels rise, even when filter capacity and efficiency remain constant.

Limitations and assumptions

This calculator intentionally simplifies how filters behave in the real world. To interpret results responsibly, keep the following assumptions and limitations in mind:

• Constant pollution level: The PM2.5 concentration is assumed to remain constant over time. In reality, pollution can vary hour by hour due to cooking, traffic, weather, windows being opened, or smoke events.
• Constant CADR: The model assumes your purifier operates at a fixed airflow. Many devices have multiple fan speeds, auto modes, and sensor-based adjustments that change CADR dynamically.
• Constant efficiency: Filter efficiency is treated as a fixed percentage. Actual efficiency can change as the filter loads with dust, as airflow changes, or as the filter media ages.
• Single-pollutant focus: Only PM2.5 is considered. The calculator does not model larger particles, ultrafine particles, gases (like VOCs or ozone), humidity effects, or odours. Filters designed to remove odours or gases may saturate on a different schedule than predicted here.
• Approximate filter capacity: The dust-holding capacity you enter may be a rough guess or an idealized laboratory value. Real filters may become noisy, visibly dirty, or cause pressure drops before they reach that theoretical capacity.
• No system leakage: The airflow is assumed to pass fully through the filter, with no bypass leaks around the filter frame or through gaps in the housing.
• Room size and mixing: The model does not explicitly account for room size or how well the air mixes in the space. Very large rooms or spaces with poor mixing can leave pockets of unfiltered air even if CADR is high.
• Health and safety: The result is not a health or safety guarantee. It is an engineering-style estimate of when the filter might reach an approximate particulate load.

Because of these factors, treat the output as a planning tool rather than a strict rule. Filters may need to be replaced earlier than the calculator suggests, especially if you notice:

• Increased dust buildup on surfaces near the purifier.
• Unusual odours or a musty smell from the device.
• Reduced airflow or increased fan noise at the same speed setting.
• Visual darkening or clogging of the filter.

Always follow the manufacturer’s recommended replacement intervals, and consider local air quality and any guidance from health or environmental agencies.

Using the calculator for planning

You can use this calculator in several ways:

• Budgeting for filter replacements: Estimate how often you may need to replace filters in a given environment and plan annual costs.
• Comparing usage patterns: See how running the purifier continuously versus only at certain times of day affects filter life.
• Assessing pollution impacts: Input higher PM2.5 levels to understand how smoke events or high-pollution days can dramatically reduce filter lifespan.
• Selecting appropriate filters: Examine how a higher-capacity filter affects replacement intervals compared with a lower-capacity option, without making any specific brand recommendations.

By experimenting with different values, you can get a better sense of the trade-offs between clean air, energy use, and how frequently you will need to replace filters in your air purifier.