Activated carbon mesh sizes: 4×8, 8×30, 12×40 and -325 explained
What mesh numbers mean on activated carbon, how particle size affects adsorption speed and pressure drop, and which size suits which application.
VMS Carbon technical team · 3 min read · Updated 31 October 2026
Activated carbon granules are described by a pair of mesh numbers, such as 8×30, and powders by a single one, such as -325. These come from standard sieves and tell you the particle size range.
How to read a mesh size
A sieve's mesh number is roughly the number of openings per inch. Higher numbers mean smaller openings.
- 8×30 means the granules pass through an 8 mesh sieve (2.36 mm openings) and are retained on a 30 mesh sieve (0.60 mm). So the particles are between about 0.6 and 2.4 mm.
- -325 (minus 325) for powder means the particles pass a 325 mesh sieve (45 microns). Specifications usually state the percentage that passes, such as "90% min passing 325 mesh".
| Mesh (US) | Opening |
|---|---|
| 4 | 4.75 mm |
| 6 | 3.35 mm |
| 8 | 2.36 mm |
| 12 | 1.70 mm |
| 16 | 1.18 mm |
| 30 | 0.60 mm |
| 40 | 0.425 mm |
| 100 | 0.150 mm |
| 200 | 0.075 mm |
| 325 | 0.045 mm |
How every lot is tested
- A sample is taken from every lot
- Iodine number: how much it can adsorb
- Methylene blue: how it takes larger molecules
- Hardness, ash and moisture go on the report
Common granular sizes and their uses
| Size | Typical use |
|---|---|
| 4×8 | gas phase, large vessels, gold heap leach, low pressure drop |
| 6×12 | gold carbon-in-pulp and carbon-in-leach |
| 8×16 | gold recovery, some water filters |
| 8×30 | municipal and industrial water, the most common water grade |
| 12×40 | drinking water filters, point-of-use, faster kinetics |
| 20×50 | cartridges and household filters |
The trade-off: speed vs flow
Smaller particles adsorb faster because molecules travel a shorter distance into each grain. That means a sharper mass-transfer zone and better use of the bed. But smaller particles also pack more tightly, raising the pressure drop and making backwashing more delicate. Larger particles let water or air pass easily but need a longer contact time.
- Gravity filters and large vessels: 8×30 is a good balance.
- Pressure filters with short contact time: 12×40 gives faster removal.
- Gas phase: 4×8 granules or 3 to 4 mm pellets keep pressure drop low.
- Gold circuits: 6×12 or 8×16 coconut granules are easy to screen out of the pulp.
Powder fineness
Powder carbon is commonly supplied at -100, -200 or -325 mesh. Finer powder adsorbs faster and disperses more evenly, but is harder to filter out and dustier to handle. For filter-press operations such as oil bleaching, the filter aid and press cloth often decide the practical fineness.
Effective size and uniformity
Water engineers also use two numbers derived from the sieve analysis:
- Effective size (D10): the opening that passes 10% of the sample.
- Uniformity coefficient (D60/D10): how even the size is; 1.9 or less is typical for water GAC.
These matter for backwash design and bed stratification. Ask for the full sieve analysis if your filter design needs it.
Choosing a size
Tell us your vessel type, flow and target, and we will propose a size. We supply wood granules in 4×8, 8×16 and 8×30, and powder at -100, -200 or -325 mesh, plus custom cuts.
Frequently asked questions
Is 8×30 finer than 12×40?
No. 12×40 is finer: its particles are between 0.425 and 1.7 mm, while 8×30 runs from 0.6 to 2.36 mm.
Why does my new GAC bed release fines?
Handling breaks some granules. Backwash a new bed before use to remove fines; harder carbons release fewer.
Can I mix two mesh sizes in one filter?
It is not recommended. Different sizes stratify after backwashing and change the flow pattern. Use one size per bed.
