Size Tolerance

What It Measures

Size tolerance — also described as size grading, particle-size distribution or size consistency — describes the range and uniformity of the physical dimensions or particle sizes of the charcoal as supplied, and how much of a consignment falls within the declared size class.

For lump charcoal this is usually expressed as a nominal size class with allowed oversize and undersize proportions; for graded or fragmented material it is expressed as a distribution across a sieve series.

Why It Matters

Size affects packing density, airflow through the fuel bed, ignition and burn behaviour, and ease of handling. Mixed or out-of-spec sizes change how an appliance performs, how much fuel fits a given volume, and how consistently a charge burns.

Because "large" and "medium" are not universal terms, a declared size class is only meaningful when it is defined numerically and paired with a method for checking conformance.

Typical Measurement Method

Size is characterised in two broad ways. For smaller or fragmented material, sieve analysis (grading) is used: the sample is passed through a stated series of sieves and the retained fractions are reported as a distribution against a declared size class and tolerance. For large irregular lump charcoal, nominal lump dimensions are measured and the oversize/undersize fractions are reported against the declared class.

Public references include the particle-size specifications and classes of the ISO 17225 series for solid biofuels and coal sieve-analysis methods such as ASTM D4749, combined with the supplier-declared nominal size and tolerance. The sample size, sieve series (or measurement rule) and acceptance criteria must be stated for a result to be verifiable.

Buyer Relevance

Buyers who specify a size class should define it with numeric upper and lower bounds and an allowed oversize/undersize percentage, and agree in advance how conformance is checked — the sieve set, the sampling method and the tolerances.

Size also interacts with other properties: surface exposure affects how quickly moisture changes, and void fraction affects airflow during burning. A size specification is therefore part of a coherent quality specification, not a stand-alone attribute.

Limitations

Lump charcoal is irregular, so any single dimension is a simplification of a real distribution; different sieve sets or sampling approaches yield different distributions.

Breakage during handling and transport can change size between loading and delivery, so an as-loaded result may not describe the load as received. Sieve-based distributions are most meaningful for graded or fragmented material and less so for large irregular lumps. This page describes methodology only and publishes no size data.

Data Source

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

Last updated: 2026-10-07

Public methods commonly referenced

• ISO 17225 series — Solid biofuels: fuel specifications and classes (particle size)
• ASTM D4749 — Sieve analysis of coal and designating coal size
• Supplier-declared nominal size classes with agreed tolerances

Standard references are given as general, publicly documented method families. Applicability, current edition and reporting basis must be confirmed with the testing laboratory for any specific report.