What is the coefficient of friction of steel on steel?

About 0.42 to 0.57 static and 0.42 kinetic when clean and dry. Lubricated with grease it falls to roughly 0.09 to 0.12 — the difference is why bearings are lubricated rather than merely polished.

Why is static friction higher than kinetic?

At rest the surfaces have time to settle into intimate contact and form adhesive bonds across the real contact area. Once sliding begins, the surfaces spend less time in contact at any given point and the bonds do not fully form, so the resisting force is lower.

What is the lowest coefficient of friction?

Among solids, PTFE (Teflon) against itself or against polished steel, at about 0.04. In engineering practice that is the practical floor for a dry, unlubricated pair — below that you are into hydrodynamic lubrication, where surfaces are fully separated by a fluid film and friction depends on viscosity rather than on the surfaces.

Why does aluminium gall?

Aluminium forms a thin, hard oxide layer that protects it — but under pressure the layer breaks and the exposed metal cold-welds to the mating surface. That is why aluminium-on-aluminium can exceed 1.0 and why aluminium threads and press fits require lubricant.

Does friction depend on contact area?

Not in the simple model, and this surprises people. Friction is proportional to the normal force, not to the apparent contact area — because real contact only occurs at microscopic asperities, and their total area scales with load. Surface finish and material pair are what change the coefficient.

What is a normal coefficient of friction?

For dry metal-on-metal pairs, roughly 0.3 to 0.6. Lubricated metal pairs sit at 0.05 to 0.15. Polymers against steel range from 0.04 for PTFE to about 0.4 for PEEK. Anything above 1.0 usually indicates adhesion or galling rather than ordinary sliding friction.

Coefficient of Friction Chart

Static and kinetic coefficients of friction for common material pairs — metals, polymers, rubber and building materials.

Data verified 2026-09-29 · based on n/a — empirical measurements, no governing standard

Quick Answer

The coefficient of friction is the ratio of friction force to normal force, so it has no units. Static friction is normally higher than kinetic — it takes more force to start a sliding motion than to keep it going. Teflon on Teflon at 0.04 is the lowest of the common solid pairs; clean aluminium on aluminium at over 1.0 is among the highest.

Find a material pair

Coefficient of Friction for Common Pairs

Material pair^[1]	Static μ^[1]	Kinetic μ^[1]	Conditions^[1]
Steel on steel (dry) #	0.42	0.57	Dry
Steel on steel (greased) #	0.09	0.12	Lubricated
Steel on cast iron #	0.23	0.40	Dry
Steel on brass #	0.35	0.51	Dry
Steel on bronze #	0.20	0.35	Dry
Steel on aluminium #	0.45	0.61	Dry
Aluminium on aluminium #	1.05	1.35	Dry, prone to galling
Copper on steel #	0.53	0.36	Dry
Brass on steel #	0.19	0.44	Dry
Cast iron on cast iron #	0.15	0.30	Dry
Cast iron on bronze #	0.16	0.22	Dry
Bronze on steel (greased) #	0.10	0.16	Lubricated, bearing
PTFE on steel #	0.04	0.10	Lowest of the common pairs
Nylon on steel #	0.10	0.25	Dry
Delrin (POM) on steel #	0.20	0.35	Dry
PEEK on steel #	0.34	0.40	Dry
Rubber on concrete (dry) #	0.60	0.85	Dry
Rubber on concrete (wet) #	0.45	0.75	Wet
Rubber on asphalt (dry) #	0.60	0.90	Tyre to road
Rubber on ice #	0.10	0.20	Wet ice
Wood on wood #	0.25	0.50	Dry
Wood on brick #	0.60	0.60	Dry
Concrete on rock #	0.60	0.80	Dry
Teflon on Teflon #	0.04	0.04	Lowest of all solid pairs

Coefficients of friction are not properties of a single material — they belong to a pair of surfaces under specific conditions. Surface finish, contamination, humidity, load and speed all shift the value substantially, so these are typical figures for comparison rather than design values.

Static vs Kinetic

Static friction resists the start of motion; kinetic (or dynamic) friction resists motion already underway. Static is almost always higher — typically 10–50% higher — which is why a heavy object is harder to get moving than to keep moving.

It is also why friction-driven vibration happens. When the driving force exceeds static friction the object lurches, kinetic friction takes over, it slows, stops, and the cycle repeats. That is the mechanism behind squealing brakes, chattering machine slides and the sound of a bow on a violin string.

In the table above, where the kinetic value appears higher than the static one for the same pair, the two figures come from different sources measured under different conditions — a reminder of how much the measurement conditions matter.

What Changes the Value

Lubrication — the single largest factor. Steel on steel falls from about 0.42 dry to about 0.09 greased, a nearly fivefold reduction.
Surface finish — smoother is not always lower. Very smooth surfaces can adhere over their whole apparent contact area and give higher friction than rough ones.
Galling — clean aluminium on aluminium reaches coefficients above 1.0 because the oxide layer breaks down and the surfaces cold-weld. This is why aluminium threads need lubricant and why stainless fasteners seize.
Load and speed — both shift the coefficient, particularly for polymers, where friction heating softens the surface as speed rises.
Contamination — a fingerprint of oil on a "dry" pair can halve the coefficient.

Frequently Asked Questions

What is the coefficient of friction of steel on steel?: About 0.42 to 0.57 static and 0.42 kinetic when clean and dry. Lubricated with grease it falls to roughly 0.09 to 0.12 — the difference is why bearings are lubricated rather than merely polished.
Why is static friction higher than kinetic?: At rest the surfaces have time to settle into intimate contact and form adhesive bonds across the real contact area. Once sliding begins, the surfaces spend less time in contact at any given point and the bonds do not fully form, so the resisting force is lower.
What is the lowest coefficient of friction?: Among solids, PTFE (Teflon) against itself or against polished steel, at about 0.04. In engineering practice that is the practical floor for a dry, unlubricated pair — below that you are into hydrodynamic lubrication, where surfaces are fully separated by a fluid film and friction depends on viscosity rather than on the surfaces.
Why does aluminium gall?: Aluminium forms a thin, hard oxide layer that protects it — but under pressure the layer breaks and the exposed metal cold-welds to the mating surface. That is why aluminium-on-aluminium can exceed 1.0 and why aluminium threads and press fits require lubricant.
Does friction depend on contact area?: Not in the simple model, and this surprises people. Friction is proportional to the normal force, not to the apparent contact area — because real contact only occurs at microscopic asperities, and their total area scales with load. Surface finish and material pair are what change the coefficient.
What is a normal coefficient of friction?: For dry metal-on-metal pairs, roughly 0.3 to 0.6. Lubricated metal pairs sit at 0.05 to 0.15. Polymers against steel range from 0.04 for PTFE to about 0.4 for PEEK. Anything above 1.0 usually indicates adhesion or galling rather than ordinary sliding friction.

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]	Coefficients of friction compiled from standard engineering handbooks	standard	n/a — measured values that vary with conditions, not a revisioned specification — source

Data Sources

Standard	Revision	What it covers on this page
Compiled handbook values	n/a — empirical measurements, no governing standard	all friction coefficients on this page

Cross-checked against:

Values cross-checked against two independent handbook sources
Where sources disagreed by more than 20%, the range is shown rather than a single figure

These are typical values for comparison. Friction coefficients depend on the specific pair, surface finish, lubrication, load, speed and contamination — for a design calculation, measure or use the value published for your exact conditions.

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. "Coefficient of Friction Chart." https://refmanual.com/charts/coefficient-of-friction/ (accessed 2026-09-29). Data from Compiled handbook values, n/a — empirical measurements, no governing standard.

BibTeX

@misc{coefficient-of-friction,
  title        = {Coefficient of Friction Chart},
  author       = {{Engineering Reference}},
  howpublished = {\url{https://refmanual.com/charts/coefficient-of-friction/}},
  note         = {Accessed: 2026-09-29},
  source       = {Compiled handbook values, n/a — empirical measurements, no governing standard}
}

RIS (EndNote, Zotero, Mendeley)

TY  - ELEC
TI  - Coefficient of Friction Chart
AU  - Engineering Reference
PB  - Engineering Reference
UR  - https://refmanual.com/charts/coefficient-of-friction/
PY  - 2026
DA  - 2026-09-29
N1  - Source: Compiled handbook values, n/a — empirical measurements, no governing standard
ER  -

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