# Spring Stiffness Calculator

**Definition:**

Spring calculation program which automatically calculates the spring stiffness (spring force) of a spring using only a few of such spring’s measurements (dimensions).

There are many spring calculators around the internet but none like Spring Creator. This spring stiffness calculator will calculate all of the values required to determine whether the spring will be stiff enough to meet its requirements. The stiffness of your spring depends on the proportion of each spring dimension with all the others. This is where spring index and space between the coils (pitch) comes in. The examples shown below the calculator will explain why your spring is either too stiff or not stiff enough.

**Spring Stiffness**

Spring stiffness is based on spring rate . It is also mostly based on proportion though. A ten pound rate may not seem like much on a large spring but on a small spring, it might be just enough. If you lower the amount of coils, you’ll increase the spring stiffness which is the spring's rate. If you adjust the outer diameter or the wire diameter, you will affect spring’s force and stiffness as well. The force chart to the right shows what adjustments you must make to a spring in order to meet a certain stiffness. It also shows what you can do if your spring is too stiff.

**The Force Chart**

**Spring Index**

Spring index is the proportional ratio between the spring’s outer diameter and wire diameter. It is basically the tightness of your spring’s coils. If your spring coils are too tight, they’re obviously under more stress thus making your spring stiffer. To calculate spring index, you must calculate the mean diameter first. This is done by subtracting one wire diameter from the outer diameter or adding one wire diameter to the inner diameter. Once you’ve calculated the mean diameter, you must divide it by one wire diameter. This calculation will provide you with your spring index thus letting you know how tight it is. The minimum spring index is of 4 to 1. On spring indexes from 27 or higher, please contact us to see if it is manufacturable.

**Spring Index Example**

**Total Coils**

The amount of coils on a spring also determines the stiffness of a spring. The less coils you have, the stiffer your spring will be. In the case of a torsion spring, less coils give you more torque but less travel. In the case of an extension spring, less coils also allow less travel due to the fact that these few coils will be the ones taking all the stress. If you add more coils, all of those coils will be working together to achieve more travel or deflection. In the case of a compression spring, it is based on the pitch in between its coils. The greater the amount of pitch in between the coils in proportion to the rest of the dimensions, the stiffer your spring shall be.