Enter the airflow rate (CFM) and the filter area (ft^2) into the Air to Cloth Ratio Calculator. The calculator will evaluate the Air to Cloth Ratio.
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Air to Cloth Ratio Formula
A/C Ratio = Q / A
- A/C Ratio = air to cloth ratio, also called filtration velocity or face velocity (ft/min or m/min)
- Q = airflow rate through the collector (CFM or m³/min)
- A = total filter cloth area (sq ft or sq m)
Use consistent units. CFM ÷ sq ft gives ft/min directly. m³/min ÷ sq m gives m/min. To convert: 1 ft/min = 0.3048 m/min.
For the bag dimensions mode, cloth area per cylindrical bag is:
A_bag = π × D × L
- D = bag diameter
- L = bag length
Total area is A_bag × number of bags. The calculation assumes clean cylindrical bags and ignores end caps. Cartridge media area is given by the manufacturer and should be used directly.
Typical A/C Ratios and What They Mean
Recommended ranges depend on cleaning method and dust characteristics. Fine, sticky, or hygroscopic dusts push the design toward the low end of each range.
| Collector Type | A/C Range (ft/min) | A/C Range (m/min) |
|---|---|---|
| Pulse Jet | 3 – 8 | 0.9 – 2.4 |
| Reverse Air | 1.5 – 3.5 | 0.46 – 1.07 |
| Shaker | 1.5 – 4 | 0.46 – 1.22 |
| Cartridge | 1 – 4 | 0.30 – 1.22 |
| Dust Type | Examples | Pulse Jet Target (ft/min) |
|---|---|---|
| Coarse | Sand, sawdust, grain | 6 – 8 |
| Average | Cement, clay, foundry | 4 – 6 |
| Fine | Carbon black, fume, lime | 3 – 4 |
| Sticky / Hygroscopic | Starch, sugar, soap | 2 – 3 |
Worked Example
A pulse jet baghouse handles 12,000 CFM with 96 bags, each 6 inches in diameter and 10 feet long.
Area per bag: π × (6/12 ft) × 10 ft = 15.71 sq ft. Total cloth area: 96 × 15.71 = 1,508 sq ft. A/C ratio: 12,000 ÷ 1,508 = 7.96 ft/min. That sits at the top of the pulse jet range. Acceptable for coarse dust, but too aggressive for fine or sticky dust. Either add bags or reduce airflow to drop into the 4 to 6 ft/min band.
FAQ
Is a higher or lower A/C ratio better? Lower is gentler on the bags. Higher reduces equipment cost but increases pressure drop, cleaning frequency, and emissions, and shortens bag life.
What is net vs. gross A/C ratio? Gross uses total cloth area. Net excludes the area of compartments offline for cleaning. For pulse jet on demand cleaning, gross and net are usually equal. For reverse air or shaker units, net is the value to compare against the design range.
Does temperature change the ratio? The cloth area does not change, but airflow does. Use the actual volumetric flow at operating temperature (ACFM), not the standard flow (SCFM).
What if my result is below the recommended range? The unit is oversized for the duty. Bag life will be long and pressure drop low, but capital cost is higher than necessary.
