Lead Hardness Scale
Pens, Inks & Leads · 6 specs
Direct Answer
The Graphite Hardness Grading Scale (standardized under ISO 15184 and ASTM D3363) classifies pencil graphite from 9H (hardest, lightest grey, highest clay content) through HB (medium equilibrium) to 9B (softest, darkest black, highest graphite content). HB is the universal writing standard and the exact equivalent to the North American No. 2 pencil.
Source: ISO 15184 (Determination of film hardness by pencil test) / ASTM D3363 / Koh-i-Noor Hardtmuth Standard · Last reviewed Aug 28, 2026
Specs
| Hard Grade Range (9H to 2H) | 9H, 8H, 7H, 6H, 5H, 4H, 3H, 2H — high clay/polymer binder ratio, crisp hairline precision, zero smudging |
| Medium Equilibrium Range (H, F, HB, B) | H (Hard), F (Fine point retention), HB (Hard Black — standard writing balance), B (Black) |
| Soft Grade Range (2B to 9B) | 2B, 3B, 4B, 5B, 6B, 7B, 8B, 9B — high graphite content, deep velvety blacks, artistic shading |
| US No. 2 Pencil Equivalent | HB grade (mandatory for optical Scantron standardized bubble test optical scanners) |
| US Numbering System Cross-Check | #1 = B | #2 = HB | #2.5 = F | #3 = H | #4 = 2H |
| Origin | Developed by Joseph Hardtmuth of Koh-i-Noor in Vienna (1790s), who introduced the H/B alphanumeric system |
Why Scantron Tests Require No. 2 / HB
Optical Mark Recognition (OMR) Scantron test scoring machines illuminate answer sheets with infrared or optical light sensors. HB / No. 2 graphite contains the precise balance of graphite opacity and reflectivity: softer grades (3B, 4B) smudge across conveyor belts creating false marks, while harder grades (2H, 3H) lack sufficient graphite mass to block the optical sensor.