Basic Extension Spring Calculation Formulas:

Sometimes, you might only have a few of your extension spring's dimensions but in order to calculate other things such as rate and travel, you'll need to know a bit more. Here you will see a couple examples of different scenarios where a certain spring dimension is needed.

**To Calculate Wire Diameter From a Spring: **

If you only have your Outer Diameter (OD) and Inner Diameter (ID) but need Wire Diameter (WD), you must subtract your Inner Diameter (ID) from your Outer Diameter (OD) and then divide the result by two as shown in the formula below:

(Outer Diameter – Inner Diameter) ÷ 2 = Wire DIameter

(OD - ID) ÷ 2 = WD

**To Calculate Your Springs Outer Diameter From Inner Diameter: **

Multiply your Wire Diameter by two and then add it to your Inner Diameter; as shown in the formula below.

2 * Wire Diameter + Inner Diameter = Outer Diameter

2WD + ID = OD

**To Calculate Your Springs Inner Diameter From Outer Diameter: **

Multiply your wire diameter by two and then subtract the result from your Outer Diameter; as shown in the following formula.

Outer Diameter – 2 * Wire Diameter = Inner Diameter

OD – 2WD = ID

**To Calculate Your Springs Mean Diameter:**** **

This specific dimension is calculated by taking one wire diameter and subtracting it from your compression spring's outer diameter or adding one wire diameter to the inner diameter as shown below.

Outer Diameter – Wire Diameter = Mean Diameter

OD – WD = MD

Inner Diameter + Wire Diameter = Mean Diameter

ID + WD = MD