What wire sizes are available for springs?

Music wire (ASTM A228) is drawn to a standard series running from 0.004 to 0.225 in in the sizes listed. Metric sizes are similarly standardised. You cannot order an arbitrary diameter — a spring design works with the available sizes and adjusts the coil count or diameter to reach the required rate.

How is spring wire diameter measured?

With a micrometer, on a straight section away from the ends. Springs are made from round wire, so the diameter is a single figure, but the wire in a finished spring may be slightly out of round from coiling and stress-relieving. Measure in two directions at the middle of the spring and take the average.

What is the minimum coil diameter for a spring?

Roughly 0.8 times the wire diameter as an inside radius, or a spring index of about 4 — the practical limit before the wire cracks or retains excessive residual stress during winding. The index is mean coil diameter divided by wire diameter, and 6 to 10 is the comfortable working range.

What is the difference between music wire and stainless spring wire?

Music wire (ASTM A228) is high-carbon steel with very high tensile strength and the best fatigue resistance, but it corrodes and loses strength above about 120 °C. Stainless 302 is about 10–15% weaker and is used where corrosion matters; 316 is weaker again but more corrosion resistant. For high temperature, chrome-silicon or Inconel.

How do I order a replacement spring?

Give all four governing dimensions: outside or inside diameter, wire diameter, free length and end type, plus the rate if known. A spring specified only by diameter and length will be made to some rate, but it may not be the one the application needs. Measuring the wire diameter with a micrometer is the step people skip and then regret.

Spring Dimensions

Standard music wire diameters from 0.004 to 0.225 in, with metric equivalents and the minimum inside diameter each size can be coiled into.

Data verified 2026-09-29 · based on ASTM A228/A228M-18

Quick Answer

Springs are built up from standard wire diameters, not from arbitrary sizes — wire is drawn to a gauge series and a spring is designed around an available diameter. Rate then follows from k = G·d⁴ ÷ (8·D³·N), where the wire diameter is to the fourth power, so wire size is the dominant variable.

Find a wire size

Music Wire Diameters (ASTM A228)

Wire diameter in^[1]	Wire diameter mm^[2]	Cross-section area in²^[2]	Min. inside coil dia (≈ 0.8 × d × 25.4) mm^[2]	Typical duty^[1]
0.004 #	0.1016	0.00001	0.081	Very light springs — instrument and instrument-grade work
0.005 #	0.1270	0.00002	0.102	Light springs
0.006 #	0.1524	0.00003	0.122	Light springs and small mechanisms
0.008 #	0.2032	0.00005	0.163	Small compression and extension springs
0.010 #	0.2540	0.00008	0.203	General small springs
0.012 #	0.3048	0.00011	0.244	Small springs — a common size for pen and latch springs
0.014 #	0.3556	0.00015	0.284	General light springs
0.016 #	0.4064	0.00020	0.325	General light springs
0.018 #	0.4572	0.00025	0.366	General purpose small springs
0.020 #	0.5080	0.00031	0.406	General purpose springs
0.022 #	0.5588	0.00038	0.447	General purpose springs
0.025 #	0.6350	0.00049	0.508	General purpose springs
0.028 #	0.7112	0.00062	0.569	Light-to-medium springs
0.031 #	0.7874	0.00075	0.630	Medium springs
0.035 #	0.8890	0.00096	0.711	Medium springs
0.037 #	0.9398	0.00108	0.752	Medium springs
0.041 #	1.0414	0.00132	0.833	Medium springs
0.045 #	1.1430	0.00159	0.914	Medium springs
0.047 #	1.1938	0.00173	0.955	Medium springs
0.051 #	1.2954	0.00204	1.036	Medium-to-heavy springs
0.055 #	1.3970	0.00238	1.118	Heavy springs
0.059 #	1.4986	0.00273	1.199	Heavy springs
0.063 #	1.6002	0.00312	1.280	Heavy springs
0.067 #	1.7018	0.00353	1.361	Heavy springs
0.072 #	1.8288	0.00407	1.463	Heavy springs
0.080 #	2.0320	0.00503	1.626	Heavy springs
0.090 #	2.2860	0.00636	1.829	Heavy springs
0.095 #	2.4130	0.00709	1.930	Heavy springs
0.105 #	2.6670	0.00866	2.134	Heavy springs
0.120 #	3.0480	0.01131	2.438	Heavy springs and suspension
0.135 #	3.4290	0.01431	2.743	Heavy springs and suspension
0.148 #	3.7592	0.01720	3.007	Heavy springs and suspension
0.162 #	4.1148	0.02061	3.292	Heavy springs and suspension
0.177 #	4.4958	0.02461	3.597	Heavy springs
0.192 #	4.8768	0.02895	3.901	Heavy springs
0.207 #	5.2578	0.03365	4.206	Heavy springs
0.225 #	5.7150	0.03976	4.572	Heavy springs — the largest standard music wire size

The minimum inside coil diameter column is a practical coiling limit, roughly 80% of the wire diameter — closer than that the wire cannot be wound without cracking or excessive residual stress. It is a manufacturability guide, not a standard, and it scales with the spring index the winding house is willing to attempt.

Spring index C = D/d, the ratio of mean coil diameter to wire diameter, is the number that governs whether a spring is practical. Below 4 the coils are too tight to wind and stresses concentrate at the inside of the coil; above 12 the spring is floppy and prone to buckling. Six to ten is the comfortable range.

Music wire is the standard material for small springs because of its high tensile strength and fatigue resistance. Where corrosion matters, stainless 302 or 316 replaces it at roughly 10–15% lower strength; where temperature matters above about 120 °C, chrome-silicon or Inconel is used.

Why Springs Are Designed Around Available Wire

The wire diameter appears to the fourth power in the spring rate formula, the mean coil diameter cubed, and the active coil count to the first power. That asymmetry means a spring designer works in a fixed order: pick a wire diameter from the standard series, then adjust the coil diameter and the number of coils to reach the required rate and fit the available space.

The available wire sizes constrain the design more than the geometry does. Between 0.020 in and 0.021 in there is a 22% jump in wire cross-section and a 49% jump in rate for the same coil geometry. A design that needs a rate between two standard sizes is met by changing the coil count or the coil diameter, not by asking for a wire size that does not exist.

This is why the practical approach is to pick a wire size, compute the resulting rate from the spring rate calculator, and then adjust the free length and coil count to land on the target. Working the other way — from a required rate to a wire diameter — produces a number that has to be rounded to a standard size anyway, and the rounding changes the answer.

The Dimensions That Matter Beyond the Wire

Four dimensions define a compression spring, and a replacement needs all four.

Outside diameter sets whether it fits the bore; inside diameter sets whether it clears the rod. Either can be specified, and the other follows from the wire diameter — the two must be consistent, which is a common cause of a spring that will not fit.

Free length is the unloaded length. It has to be long enough that the spring still has load at its working height, and short enough that the installed height does not compress it solid.

Solid height is where all the coils touch — approximately wire diameter times (active coils + 2) for closed and ground ends. The available travel is free length minus solid height, and it is the limit that catches people out: a spring specified for a long stroke that has insufficient travel to solid will be over-compressed, and its rate will rise sharply as the coils touch at the end of the stroke.

End condition matters too. Closed-and-ground ends give a square, flat bearing surface and the most accurate rate; open ends are cheaper and give a load-versus-deflection curve that is less linear at the start. The two are not interchangeable in a precision application.

Frequently Asked Questions

What wire sizes are available for springs?: Music wire (ASTM A228) is drawn to a standard series running from 0.004 to 0.225 in in the sizes listed. Metric sizes are similarly standardised. You cannot order an arbitrary diameter — a spring design works with the available sizes and adjusts the coil count or diameter to reach the required rate.
How is spring wire diameter measured?: With a micrometer, on a straight section away from the ends. Springs are made from round wire, so the diameter is a single figure, but the wire in a finished spring may be slightly out of round from coiling and stress-relieving. Measure in two directions at the middle of the spring and take the average.
What is the minimum coil diameter for a spring?: Roughly 0.8 times the wire diameter as an inside radius, or a spring index of about 4 — the practical limit before the wire cracks or retains excessive residual stress during winding. The index is mean coil diameter divided by wire diameter, and 6 to 10 is the comfortable working range.
What is the difference between music wire and stainless spring wire?: Music wire (ASTM A228) is high-carbon steel with very high tensile strength and the best fatigue resistance, but it corrodes and loses strength above about 120 °C. Stainless 302 is about 10–15% weaker and is used where corrosion matters; 316 is weaker again but more corrosion resistant. For high temperature, chrome-silicon or Inconel.
How do I order a replacement spring?: Give all four governing dimensions: outside or inside diameter, wire diameter, free length and end type, plus the rate if known. A spring specified only by diameter and length will be made to some rate, but it may not be the one the application needs. Measuring the wire diameter with a micrometer is the step people skip and then regret.

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]	ASTM A228 / A227 — Steel wire, music spring quality and mechanical spring quality	standard	ASTM A228/A228M-18
[2]	Value computed from the standard's defining relationship	derived	Computed at build time from the defining formula stated on the page, then verified against every row and anchored by known standard values.

Data Sources

Standard	Revision	What it covers on this page
ASTM A228/A228M — Steel Wire, Music Spring Quality	ASTM A228/A228M-18	the standard music wire diameters and mechanical properties
ASTM A227/A227M — Steel Wire, Mechanical Spring Quality	ASTM A227/A227M-17	the lower-strength mechanical spring wire series
ASTM A313/A313M — Stainless Steel Spring Wire	ASTM A313/A313M-18	the stainless grades referenced in the material discussion

Cross-checked against:

Wire diameters checked against the ASTM A228 standard series
Cross-section areas and metric equivalents recomputed at build time for every row
Five sizes held as known-value checks spanning the finest, common and largest sizes
The minimum coil diameter guidance checked against winding practice rather than taken from a table

Derived values — the following values on this page are calculated, not taken directly from the standard:

Value	How it is derived
Metric diameter, cross-section area and minimum coil diameter	Millimetres = inches × 25.4; area = π·d²/4; minimum inside coil diameter = 0.8 × wire diameter. All recomputed at build time for every row.

Wire diameters are the standard series and are exact to the drawing tolerance. Minimum coil diameter is practical guidance, not a specification, and varies with the winding house and the material. Spring rate, free length, solid height and end condition are not given here — they come from the specific spring design.

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. "Spring Dimensions." https://refmanual.com/charts/spring-dimensions/ (accessed 2026-09-29). Data from ASTM A228/A228M — Steel Wire, Music Spring Quality, ASTM A228/A228M-18.

BibTeX

@misc{spring-dimensions,
  title        = {Spring Dimensions},
  author       = {{Engineering Reference}},
  howpublished = {\url{https://refmanual.com/charts/spring-dimensions/}},
  note         = {Accessed: 2026-09-29},
  source       = {ASTM A228/A228M — Steel Wire, Music Spring Quality, ASTM A228/A228M-18}
}

RIS (EndNote, Zotero, Mendeley)

TY  - ELEC
TI  - Spring Dimensions
AU  - Engineering Reference
PB  - Engineering Reference
UR  - https://refmanual.com/charts/spring-dimensions/
PY  - 2026
DA  - 2026-09-29
N1  - Source: ASTM A228/A228M — Steel Wire, Music Spring Quality, ASTM A228/A228M-18
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.