Inputs
Wire diameter d (0.30 to 15.00 mm) and grade SL, SM, DM, SH or DH select the row and column of Table 3.
Springs · material
Spring Wire Strength to EN 10270-1
Cold-drawn spring steel wire has no single tensile strength: it falls as wire diameter grows, because the drawing process strengthens a thinner cross-section more. This calculator returns the Rm range tabulated in EN 10270-1 Table 3 for a chosen diameter and grade -- as an input helper for the spring and torsion-spring calculators.
Use the resulting strength directly in a calculation: Compression Spring Calculator, Extension Spring Calculator or Torsion Spring Calculator.
EN10270-1
02
Tensile strength
Enter diameter and wire grade.
Inputs and method
Spring wire tensile strength to EN 10270-1
Determine the tensile-strength range tabulated in Table 3 of cold-drawn spring steel wire for a diameter and grade.
Calculation
A pure table lookup: diameter selects the row band, grade the column. DM always carries the same value as SM, DH the same as SH -- Annex A.4 of the standard states explicitly that both grade pairs share the same tensile strength.
Example
A 2.5 mm wire in grade SM lies between 1690 MPa and 1890 MPa per Table 3, mean 1790 MPa. The same diameter in SH lies between 1900 MPa and 2110 MPa.
Sources and limits: DIN EN 10270-1:2024-06, Table 3 (mechanical properties). SL/SH values are not tabulated at every diameter; outside the 0.30-15.00 mm range covered here, consult the printed table.
Spring wire tensile strength to EN 10270-1 in detail
Determine the tensile-strength range tabulated in Table 3 of cold-drawn spring steel wire for a diameter and grade.
Why doesn't spring wire have a fixed tensile strength?
Cold-drawn spring steel wire reaches its final diameter through several drawing passes, and each pass work-hardens the material. For thin wire, the same drawing process affects the cross-section proportionally more than for thick wire, so achievable tensile strength falls as diameter grows -- a 1 mm SM wire reaches roughly 1960 to 2200 MPa, a 10 mm wire of the same grade only 1240 to 1400 MPa. Assuming a constant Rm regardless of diameter therefore produces wrong results in spring calculations across varying wire sizes.
Formula and variables
A pure table lookup: diameter selects the row band, grade the column. DM always carries the same value as SM, DH the same as SH -- Annex A.4 of the standard states explicitly that both grade pairs share the same tensile strength.
Choose the inputs correctly
Wire diameter d (0.30 to 15.00 mm) and grade SL, SM, DM, SH or DH select the row and column of Table 3.
How to use the calculator
Enter wire diameter and the desired grade. The calculator returns minimum, maximum and mean tensile strength; the mean is a reasonable starting value for the spring calculators when no test certificate with the actual Rm is available.
Worked example
A 2.5 mm wire in grade SM lies between 1690 MPa and 1890 MPa per Table 3, mean 1790 MPa. The same diameter in SH lies between 1900 MPa and 2110 MPa.
How accurate is the mean value?
Rm spreads by up to 260 MPa between minimum and maximum within one row -- that is not this calculator's uncertainty but the manufacturing scatter of rolled steel that the standard itself permits. For a preliminary spring calculation the mean is a defensible starting point; for a load-bearing strength verification, use the certified Rm of the wire actually delivered (mill certificate), not the table mean.
Diameter in millimetres, tensile strength in MPa.
Typical applications
Determining a plausible starting Rm for the compression, extension and torsion spring calculators when no test certificate is available; checking whether an existing certificate falls within the normative range.
Assumptions, limits and common mistakes
DIN EN 10270-1:2024-06, Table 3 (mechanical properties). SL/SH values are not tabulated at every diameter; outside the 0.30-15.00 mm range covered here, consult the printed table.
Common mistake: Don't carry over the Rm value of one diameter unchanged to another diameter of the same grade -- the table is not linearly stepped. Nor should SL, SM and SH be used as a label divorced from the actual test certificate: for safety-relevant designs the certified Rm of the delivered wire governs, this calculator only gives the normative range.
Frequently asked questions
Why does tensile strength depend on wire diameter?
Because the cold-drawing process that produces the high strength work-hardens thinner wire proportionally more per cross-section. Rm therefore falls consistently with growing diameter -- from above 2500 MPa for very thin wire to below 1300 MPa at 15 mm.
Which wire grade should I choose?
That depends on the load case, not a blanket recommendation: SL for moderately loaded static springs, SM for most applications, SH for highly loaded static springs; DM and DH are oil-hardened variants for a similar range of use. Dynamically loaded springs additionally require a fatigue assessment to EN 13906-1.
Are DM and SM really always equally strong?
Yes, per Annex A.4 of the standard, grade DM always has the same tensile strength as SM and DH the same as SH -- confirmed by every row of the table used here. The difference is the manufacturing route (oil-hardened and tempered instead of patented and drawn), not the strength.