The image above represents stiffness performance index.

To compute for stiffness performance index, two essential parameters are needed and these parameters are **Shear Modulus (G)** and **Density (ρ).**

The formula for calculating stiffness performance index:

P = ^{√(G)}/_{ρ}

Where:

P = Stiffness Performance Index

G = Shear Modulus

ρ = Density

Let’s solve an example;

Find the stiffness performance index when the shear modulus is 36 and the density is 12.

This implies that;

G = Shear Modulus = 36

ρ = Density = 12

P = ^{√(G)}/_{ρ}

P = ^{√(36)}/_{12}

P = ^{6}/_{12}

P = 0.5

Therefore, the **stiffness performance index **is **0.5**

**Calculating the Shear Modulus when the Stiffness Performance Index and the Density is Given.**

G = (P x ρ)^{2}

Where:

G = Shear Modulus

P = Stiffness Performance Index

G = Shear Modulus= Stiffness Performance Index

ρ = Density

Let’s solve an example;

Find the shear modulus when the stiffness performance index is 25 and the density is 5.

This implies that;

P = Stiffness Performance Index = 25

ρ = Density = 5

G = (P x ρ)^{2}

G = (25 x 5)^{2}

G = 15,625

Therefore, the **shear modulus **is **15,625.**

**Calculating the Density when the Stiffness Performance Index and Shear Modulus is Given.**

ρ = ^{√(G)} / _{P}

Where;

ρ = Density

P = Stiffness Performance Index

G = Shear Modulus

Let’s solve an example;

Find the density when the stiffness performance index is 4 and the shear modulus is 64.

This implies that;

P = Stiffness Performance Index = 4

G = Shear Modulus = 64

ρ = ^{√(G)} / _{P}

ρ = ^{√64} / _{4}

ρ = ^{8} / _{4}

ρ = 2

Therefore, the **density **is **2.**

Nickzom Calculator – **The Calculator Encyclopedia** is capable of calculating the stiffness performance index.

To get the answer and workings of the stiffness performance index using the **Nickzom Calculator – The Calculator Encyclopedia. **First, you need to obtain the app.

You can get this app via any of these means:

**Web** – https://www.nickzom.org/calculator-plus

To get access to the **professional **version via web, you need to **register** and **subscribe **for** NGN 2,000 **per** annum** to have utter access to all functionalities.

You can also try the **demo **version via https://www.nickzom.org/calculator

**Android (Paid)** – https://play.google.com/store/apps/details?id=org.nickzom.nickzomcalculator

**Android (Free)** – https://play.google.com/store/apps/details?id=com.nickzom.nickzomcalculator

**Apple (Paid)** – https://itunes.apple.com/us/app/nickzom-calculator/id1331162702?mt=8

Once, you have obtained the calculator encyclopedia app, proceed to the **Calculator Map, **then click on **Materials and Metallurgical **under **Engineering****.**

Now, Click on **Material Selection**** **under **Materials and Metallurgical**

Now, Click on **Stiffness ****Performance Index **under **Material Selection**

The screenshot below displays the page or activity to enter your values, to get the answer for the stiffness performance index according to the respective parameter which is the **Shear Modulus (G)** and **Density (ρ).**

Now, enter the values appropriately and accordingly for the parameters as required by the **Shear Modulus (G)** is **36 **and **Density (ρ)** is **12**.

Finally, Click on Calculate

As you can see from the screenshot above, **Nickzom Calculator**– The Calculator Encyclopedia solves for the stiffness performance index and presents the formula, workings and steps too.