Air-to-Cloth Ratio

What Is Air-to-Cloth Ratio?

Air-to-cloth ratio, often abbreviated as A/C ratio, describes how much air passes through each unit of effective filter area in a dust collector.

It compares the total airflow of the system with the usable surface area of the filter bags or cartridges. In metric units, air-to-cloth ratio is normally expressed in meters per minute (m/min). In imperial units, it is expressed in feet per minute (ft/min).

For example, an air-to-cloth ratio of 1.0 m/min means that each square meter of effective filter area handles approximately one cubic meter of air per minute.

A higher air-to-cloth ratio means that more air passes through the same amount of filter media. This can reduce the required filter area and make the dust collector more compact. However, it also increases the filtration load and may lead to:

• Higher differential pressure
• More frequent filter cleaning
• Faster dust cake buildup
• Reduced system airflow
• Shorter filter life

A lower air-to-cloth ratio provides more filter area for the same airflow. This generally reduces the load on the filter media and helps maintain a more stable pressure drop, but it also requires a larger dust collector.

There is no single air-to-cloth ratio suitable for every application. The correct value depends on the dust characteristics, dust concentration, filter media, cleaning method, temperature, moisture and required emission level.

Air-to-Cloth Ratio Formula

Air-to-cloth ratio is calculated by dividing the airflow through the dust collector by the total effective filter area.

Air-to-Cloth Ratio = Airflow ÷ Total Effective Filter Area

The formula can also be written as:

A/C = Q ÷ A

Where:

• A/C = Air-to-cloth ratio
• Q = Airflow through the dust collector
• A = Total effective filter area

When airflow is expressed in cubic meters per hour, it must first be converted into cubic meters per minute.

Air-to-Cloth Ratio (m/min) = Airflow (m³/h) ÷ 60 ÷ Filter Area (m²)

When airflow is expressed in actual cubic feet per minute and filter area is expressed in square feet, the result is given in feet per minute.

Air-to-Cloth Ratio (ft/min) = Airflow (ACFM) ÷ Filter Area (ft²)

The calculation should use the effective filter area that is actually available during operation. For collectors using offline cleaning, the available online filter area may be lower than the total installed filter area.

Air-to-Cloth Ratio Calculation Example

Assume a baghouse dust collector has the following design parameters:

• System airflow: 15,000 m³/h
• Total effective filter area: 250 m²

First, convert the airflow from cubic meters per hour to cubic meters per minute:

15,000 ÷ 60 = 250 m³/min

Then divide the converted airflow by the total effective filter area:

250 m³/min ÷ 250 m² = 1.0 m/min

The calculated air-to-cloth ratio is:

1.0 m/min

This means that each square meter of effective filter area handles approximately one cubic meter of air per minute.

The result shows the filtration load of the dust collector, but it does not by itself confirm whether the system design is suitable. The final design value should still be selected according to the dust properties, filter media, cleaning system and operating conditions.

Air-to-Cloth Ratio Calculator

Use the calculator below to estimate the air-to-cloth ratio of a baghouse or cartridge dust collector.

Enter the system airflow and total effective filter area. The calculator will automatically convert the selected units and display the calculated air-to-cloth ratio.