Spring rate, previously also known as spring ratio or spring constant, is the quotient of the spring force and the spring excursion (cf. springs). For cylindrical helical compression springs, the following formula applies:

R = = [N/mm]

R = Spring rate

DF = D Spring force

Ds = D Spring excursion

G = Thrust modulus in N/mm²

d = Wire diameter

D = Mean coil diameter

n = Number of effective spring coils