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Sharpness Scale

  

This Sharpness Scale is used as a way to define relative sharpness, especially for tools which are not needing to be “razor sharp”.

Please also note, these are for linear edges, not for pointed objects (e.g., needles).

General Guidelines

Rating

Definition

Measurement

Comments & Examples

Edge Radius

BESS1

REST2

0

 Totally blunt Width ≥ 2mm Width ≥ 1/16”    

Flat edge

  • Practice Swords

1

 Blunt ≥ 2.5mm
≥ 3/32” 		   

Rounded edge

2

 Dull 0.5mm - 2.5mm
3/128” - 3/32” 		2,000  

Rounded edge

  • Butter knife

3

 Dirty sharp < 0.5mm
< 3/128” 		   

Dull edge, coming to a “point”

  • Gardening tools for digging into dirt
  • Masonry drill bits
  • Metalworking bench tools

4

 Heavy duty sharp      
  • Metal lathe tools

5

 Generally sharp      
  • Drilling bits, other than masonry bits
  • Gardening tools for cutting (e.g., secateurs)

6

 High speed sharp   200 - 400 2N - 4N
  • Handsaw blades
  • Scissors
  • Woodturning tools

7

 High volume sharp   100 - 200 1N - 1.8N
  • Kitchen knives
  • Woodturning skews

8

 Razor sharp   50 - 100 0.5N - 1N
  • Razors
  • Woodworking bench tools

9

 Surgical sharp   ≤ 50 ≤ 0.4N
  • Surgical scalpels

10

 Sharpest physically possible 1 atom wide at cutting edge    

This is more theoretical than can be actually achieved. There is nothing known to be in this category at this time.

Notes

  1. BESS is an acronym for Brubacher Edge Sharpness Scale. BESS-calibrated edge sharpness testers show edge apex radius in nm. Commercial safety razors score 50 on the tester and have a 50 nm apex radius. A score of 100 equates to a 0.1 micron edge apex width.
  2. REST is an acronym for the Cutlery & Applied Trades Research Association (CATRA)'s Razor Edge Sharpness Tester. It is a measure of the push-cutting force in Newtons.

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