What is a machinability rating?

A comparative percentage describing how easily a material can be cut, on a scale where AISI 1112 free-machining steel is 100%. It folds together chip formation, surface finish, tool wear and power consumption into one shop-floor number.

Which metal is easiest to machine?

Among common metals, free-cutting brass and aluminium 6061 rate highest at about 300% on this scale. Of steels, leaded 12L14 at 170% is the easiest. The ratings above 100% reflect both softness and built-in chip breaking.

Why is stainless steel harder to machine than carbon steel?

Two reasons: it work-hardens rapidly, so a cut that rubs rather than shears leaves a harder surface behind, and it conducts heat poorly, so heat concentrates at the cutting edge instead of being carried away by the chip. Ratings of 36–78% reflect that.

What is the most difficult metal to machine?

Of the materials on this site, Inconel 718 at 10% is the most difficult. Nickel superalloys combine severe work-hardening, poor thermal conductivity and abrasiveness, and they hold strength at the temperatures generated by cutting.

Does a higher machinability rating mean a faster cutting speed?

Broadly yes, but not proportionally. The rating is a ranking, not a speed multiplier. Use the cutting speed table on each material page as the starting point, and adjust for the insert grade, depth of cut, rigidity and coolant.

Machinability Rating Chart

Machinability ratings for the metals on this site, on the scale where free-machining steel is 100% — with material group, hardness and typical roughing speed.

Data verified 2026-09-29 · based on n/a — industry comparison scale with no single governing standard

Quick Answer

Machinability is a comparison scale, not a physical property: AISI 1112 free-machining steel is defined as 100%. Ratings above 100% cut more easily — aluminium 6061 rates 300%, leaded steel 12L14 rates 170%. Ratings below 100% are harder to cut — Inconel 718 rates 10%.

Find a material

Machinability Ratings (AISI 1112 = 100%)

Material^[1]	Group^[1]	Machinability^[1]	Hardness^[1]	Typical roughing^[1]
Aluminium 6061-T6 #	N	300 %	95 HB	1,000–1,500 SFM
Brass 360 #	N	300 %	78 HRB	600–1,000 SFM
Aluminium 5052 #	N	250 %	60 HB	1,200–1,800 SFM
Aluminium 2024-T4 #	N	200 %	120 HB	900–1,400 SFM
AISI 12L14 #	P	170 %	130 HB	400–600 SFM
Aluminium 7075-T6 #	N	150 %	150 HB	800–1,200 SFM
AISI 1018 #	P	78 %	126 HB	300–400 SFM
AISI 303 #	M	78 %	160–200 HB	250–350 SFM
AISI 1141 #	P	72 %	190–230 HB	300–400 SFM
Gray Iron Class 30 #	K	70 %	187–241 HB	250–400 SFM
AISI 8620 #	P	66 %	150–200 HB	250–350 SFM
Ductile Iron 65-45-12 #	K	60 %	170–210 HB	200–350 SFM
AISI 1045 #	P	57 %	170–210 HB	250–350 SFM
AISI 4140 #	P	56 %	197–235 HB (annealed)	200–300 SFM
AISI 4340 #	P	50 %	217–255 HB (annealed)	180–280 SFM
17-4 PH #	M	48 %	28–38 HRC	120–200 SFM
AISI 304 #	M	45 %	170–200 HB	100–150 SFM
H13 Tool Steel #	P	45 %	190–230 HB (annealed)	150–250 SFM
O1 Tool Steel #	P	42 %	190–220 HB (annealed)	150–250 SFM
AISI 52100 #	P	40 %	190–230 HB (spheroidised)	150–250 SFM
AISI 440C #	M	40 %	56–60 HRC hardened	100–180 SFM
D2 Tool Steel #	P	38 %	210–240 HB (annealed)	120–200 SFM
AISI 316 #	M	36 %	170–210 HB	80–120 SFM
Monel 400 #	S	36 %	120–150 HB	120–200 SFM
Ti-6Al-4V #	S	22 %	33–36 HRC	120–180 SFM
Copper C11000 #	N	20 %	45 HRB	300–500 SFM
Inconel 625 #	S	15 %	30–35 HRC	80–120 SFM
Inconel 718 #	S	10 %	38–42 HRC	60–100 SFM

Ratings compare how easily a material cuts, folding together chip formation, surface finish, tool wear and power consumption. Sources differ by roughly ±10%, because each was measured under different conditions. A high rating does not mean soft — gray cast iron rates 70% and cuts easily because the graphite breaks chips, while pure copper rates 20% and is soft but gummy.

What the Rating Is and Is Not

The scale is comparative and empirical. It was built from shop-floor measurements against a reference material, and it is not derived from any physical property — which is why you cannot compute it from hardness, and why two materials of similar hardness can rate very differently.

What it is good for: ranking candidate materials when choosing between them. What it is not good for: predicting a cutting speed. For that, use the individual material page, which gives speeds by operation, and your own tooling catalogue.

Material Groups

Alongside the rating, materials are classified into groups that describe machining behaviour. Insert grades are selected by group rather than by individual alloy:

P — Steel, including alloy and tool steels. The largest group.
M — Stainless steel, austenitic and duplex. Work-hardening.
K — Cast iron. Graphite acts as a chip breaker, so it machines well despite hardness.
N — Non-ferrous: aluminium, copper, brass. Fast cutting, gummy chips.
S — Superalloys and titanium. Heat-resistant, work-hardening, the most difficult group.
H — Hardened materials, above roughly 45 HRC.

Frequently Asked Questions

What is a machinability rating?: A comparative percentage describing how easily a material can be cut, on a scale where AISI 1112 free-machining steel is 100%. It folds together chip formation, surface finish, tool wear and power consumption into one shop-floor number.
Which metal is easiest to machine?: Among common metals, free-cutting brass and aluminium 6061 rate highest at about 300% on this scale. Of steels, leaded 12L14 at 170% is the easiest. The ratings above 100% reflect both softness and built-in chip breaking.
Why is stainless steel harder to machine than carbon steel?: Two reasons: it work-hardens rapidly, so a cut that rubs rather than shears leaves a harder surface behind, and it conducts heat poorly, so heat concentrates at the cutting edge instead of being carried away by the chip. Ratings of 36–78% reflect that.
What is the most difficult metal to machine?: Of the materials on this site, Inconel 718 at 10% is the most difficult. Nickel superalloys combine severe work-hardening, poor thermal conductivity and abrasiveness, and they hold strength at the temperatures generated by cutting.
Does a higher machinability rating mean a faster cutting speed?: Broadly yes, but not proportionally. The rating is a ranking, not a speed multiplier. Use the cutting speed table on each material page as the starting point, and adjust for the insert grade, depth of cut, rigidity and coolant.

Value Sources

Each data column on this page is tied to the source it came from. The numbers in square brackets correspond to the table headers above.

#	Source	Type	Revision / method
[1]	Machinability ratings compiled from published machinability charts	standard	n/a — industry comparison scale, no governing standard — source

Data Sources

Standard	Revision	What it covers on this page
Machinability rating, AISI 1112 = 100%	n/a — industry comparison scale with no single governing standard	all ratings, hardness values and roughing speeds on this page

Cross-checked against:

Each rating cross-checked against the individual material page on this site, which is sourced independently
Ratings cross-checked against published machinability charts from two sources

Ratings are comparative and vary by roughly ±10% between sources. They rank materials; they do not predict cutting speeds. Use the material data sheet for speeds.

Accuracy and use. The values on this page are compiled from the published standards and cross-checked sources listed above. Where values are derived, the derivation is stated. No warranty, express or implied, is made as to the accuracy or completeness of this information, and no liability is accepted for any loss or damage arising from its use. Engineering reference data is provided for guidance in preliminary work — before a value is used for design, fabrication or acceptance testing, verify it against the current revision of the governing standard and against your own inspection. The user assumes all risk and responsibility in connection with the use of this information.

Cite This Page

Every value on this page is traceable to the sources listed above. If you use the data in a document, paper or report, cite it as:

Plain text

Engineering Reference. "Machinability Rating Chart." https://refmanual.com/charts/machinability/ (accessed 2026-09-29). Data from Machinability rating, AISI 1112 = 100%, n/a — industry comparison scale with no single governing standard.

BibTeX

@misc{machinability,
  title        = {Machinability Rating Chart},
  author       = {{Engineering Reference}},
  howpublished = {\url{https://refmanual.com/charts/machinability/}},
  note         = {Accessed: 2026-09-29},
  source       = {Machinability rating, AISI 1112 = 100%, n/a — industry comparison scale with no single governing standard}
}

RIS (EndNote, Zotero, Mendeley)

TY  - ELEC
TI  - Machinability Rating Chart
AU  - Engineering Reference
PB  - Engineering Reference
UR  - https://refmanual.com/charts/machinability/
PY  - 2026
DA  - 2026-09-29
N1  - Source: Machinability rating, AISI 1112 = 100%, n/a — industry comparison scale with no single governing standard
ER  -

Each row in the tables above also has a permanent link — hover a row and use the # link to cite a single value rather than the whole page.