Charcoal Hub Data

Specification methodology

Fixed Carbon in Charcoal

What fixed carbon measures, why it is calculated rather than tested directly, and how it relates to burn quality and to the other proximate-analysis figures.

Metric Fixed carbon — the solid carbon fraction remaining after moisture, volatile matter and ash are accounted for, normally calculated by difference.
Last updated 2026-10-07
Data source Public standard methodology (general); not supplier-specific test data
Methodology only — no supplier test data.

This page describes a public standard measurement in general terms. It contains no Charcoal Hub test result and no supplier-specific value. Figures for a real batch come from a laboratory report on that batch.

What It Measures

Fixed carbon is the solid carbonaceous fraction of the fuel: what remains after moisture and volatile matter are driven off, excluding the ash that will not burn. In charcoal analysis it is calculated rather than measured directly — fixed carbon = 100% - (moisture % + volatile matter % + ash %), with all four parts reported on the same basis.

Why It Matters

Fixed carbon is the closest thing to a single proxy for how much of the material behaves like charcoal: it is the fraction that burns as a glowing ember. A fuel with higher fixed carbon generally holds heat longer and gives a more sustained ember; a fuel with more volatile matter lights and flames up quickly but can burn down faster. Because it is derived, it also works as a consistency check — if a supplier reports moisture, volatile matter, ash and fixed carbon, the four figures should reconcile.

Typical Measurement Method

Fixed carbon is derived, not tested. The laboratory determines moisture (oven drying), volatile matter (heating in a covered crucible that excludes air) and ash (combustion of the residue) — the three measured components of proximate analysis, using the ASTM D1762-style approach for wood charcoal or the general solid-biofuel methods (ISO 18134 for moisture, ISO 18123 for volatile matter, ISO 18122 for ash) — and calculates fixed carbon by difference. The result therefore inherits the measurement uncertainty of all three inputs and must be reported on the same basis as they are.

Buyer Relevance

Fixed carbon is worth asking for whenever a supplier quotes volatile matter and ash separately, because the arithmetic should reconcile. A stated fixed carbon that cannot be reconstructed from the other three figures is a signal that the reported numbers came from different samples, different methods or a marketing datasheet rather than a laboratory report. For hookah charcoal, buyers usually weigh fixed carbon together with ash content rather than looking at either one alone.

Limitations

Because it is calculated by difference, fixed carbon absorbs the errors of the other three measurements and cannot be verified on its own. It says nothing about particle size, shape, density, airflow or the binder used in briquette manufacture — all of which change real burn behaviour. Two charcoals with the same fixed carbon can still burn very differently, so it is a comparative indicator rather than a performance guarantee.

Data Source

Public standard methodology (general); not supplier-specific test data

  • Method family cited in general terms only; no laboratory result is published here.
  • Last updated 2026-10-07.
  • Measurement uncertainty applies to any real figure derived by these methods and should be reported with it.

Reading the proximate-analysis set together

Fixed carbon is only as good as the three measurements it is derived from: moisture, volatile matter and ash content. Ask for all four on one basis; if they do not sum to 100% (dry basis) the set is internally inconsistent.

What a buyer should ask for

  • All four proximate figures, on one stated basis.
  • The method and laboratory used.
  • Confirmation that the values come from the same sample or batch composite.

For lab-side detail on how these fractions are obtained, see the testing sub-site; for a batch datasheet, request a quote.

Where to go next