Activated Carbon Grade Selector — Iodine · CTC · BET Index Guide
Pick an application and set your minimum iodine number to see which carbon grades match. Below the selector, a reference table shows how iodine number, CTC value, and BET surface area typically relate — with an honest disclaimer: these indices correlate, but there is no precise universal conversion between them.
Iodine number, CTC, and BET surface area all track pore development and rise together, but there is no universal conversion between them — the relationship depends on the carbon type and pore-size distribution. Match the index your application actually specifies (iodine for micropore water grades, CTC for gas/vapor, BET for research) rather than converting one to another. Send your target spec for a datasheet-backed match.
Why There Is No Universal Iodine → CTC → BET Conversion
All three indices — iodine number (mg/g), CTC activity (wt%), and BET surface area (m²/g) — measure aspects of pore development in activated carbon. They rise together as activation increases, which is why you see rough correlations online. But the exact relationship depends on pore-size distribution, which varies by raw material (coconut shell vs coal vs wood) and activation method (steam vs chemical).
Iodine number primarily reflects micropore volume (pores < 2 nm). CTC captures a broader pore range including small mesopores. BET surface area includes micropores, mesopores, and some macropore surface. A coconut shell carbon with 1000 mg/g iodine will typically have a higher CTC than a coal-based carbon at the same iodine number, because coconut shell naturally develops a narrower, more microporous structure that is also efficient for CTC molecules. Converting one number to another without knowing the carbon type introduces real error — enough to cause a wrong grade selection.
Typical Index Ranges by Grade Level
The table below shows where iodine, CTC, and BET typically fall for each grade level. These are spec-sheet ranges from our product line, not universal conversion factors. Use them for orientation, not for substituting one test for another.
| Grade Level | Iodine (mg/g) | CTC (wt%) | BET (m²/g) | Typical Applications |
|---|---|---|---|---|
| Standard | 700–850 | 40–50% | 700–900 | Municipal water, dechlorination |
| High-activity | 900–1050 | 50–60% | 900–1100 | Drinking water, general air |
| Premium | 1050–1150 | 60–70% | 1050–1200 | Gold recovery, VOC, polishing |
| Ultra | 1150–1300 | 70–80% | 1150–1400 | Solvent recovery, specialty |
Which Index Should You Specify?
| If Your Application Is… | Specify This Index | Why |
|---|---|---|
| Water treatment / drinking water | Iodine number (mg/g) | Industry standard, correlates with micropore adsorption in liquid phase |
| Air purification / solvent recovery | CTC value (wt%) | Gas-phase benchmark, measures vapor adsorption capacity directly |
| Gold recovery (CIL/CIP/CIC) | K-value & R-value | Gold loading capacity and kinetics matter more than iodine or CTC |
| Research / advanced characterization | BET surface area (m²/g) | Most complete pore-structure picture, but requires lab instrument |
| Food / pharma decolorization | Methylene blue + iodine | MB measures mesopore capacity for large color molecules; iodine covers micropores |
Related Resources
Frequently Asked Questions
Can you convert iodine number to CTC or BET surface area?
Not precisely. Iodine number, CTC (carbon tetrachloride activity), and BET surface area all rise with increasing pore development, so they are positively correlated. But the exact relationship depends on the carbon type, raw material, and pore-size distribution. Coconut shell carbon with 1000 mg/g iodine may have a different CTC and BET than a coal-based carbon at the same iodine number. Use the index your application standard actually specifies — iodine for water treatment, CTC for vapor-phase — rather than converting between them.
What iodine number do I need for water treatment?
For municipal drinking water, 800–1050 mg/g is standard. PFAS removal benefits from higher-activity carbon at 1000+ mg/g. Industrial wastewater polishing can often use 700–900 mg/g coal-based grades. The selector above filters our product range by your minimum iodine requirement and application to narrow the options.
What is CTC value and when does it matter?
CTC (carbon tetrachloride activity, expressed as a weight percentage) measures adsorption capacity in the gas/vapor phase. It matters most for air purification, solvent recovery, and VOC abatement — applications where the contaminant arrives as a vapor, not dissolved in water. Typical CTC ranges from 40% for standard grades to 80%+ for high-activity solvent recovery carbons.
What BET surface area should activated carbon have?
BET surface area (m²/g) measures total internal surface using nitrogen adsorption. Typical activated carbons range from 700 to 1,400 m²/g. Higher is not always better: what matters is the right pore-size distribution for your target molecule. Our iodine number guide, CTC guide, and BET guide go deeper into each index — links are below.
How do I choose between coconut shell, coal, and wood-based carbon?
Coconut shell carbon has the most micropores (best for small molecules, gold recovery, drinking water). Coal-based carbon has a broader pore mix (good for general water and air). Wood-based carbon has more mesopores (better for large molecules like color bodies in food processing). The selector lets you filter by raw material to compare grades side by side.
Which index should I put in a purchase specification?
Use the index your industry standard or equipment designer specifies. Water treatment buyers typically specify iodine number. Vapor-phase buyers specify CTC. Research and high-spec buyers use BET. Mixing indices or converting between them introduces uncertainty. Send us your spec and we will match it to a grade with a COA.