This article demonstrates how to calculate Specific Gravity (SG) from different density or pressure gradient in both oilfield and metric unit.

**Calculate Specific Gravity from Mud Weight In Oilfield Unit**

## 1. Calculate specific gravity using mud weight in PPG

Specific Gravity (SG) = mud weight in ppg ÷ 8.33

**Example: **

Mud weight = 13.0 ppg

Specific Gravity (SG) = 13.0 ppg ÷ 8.33

Specific Gravity (SG)= 1.56

## 2. Calculate specific gravity using pressure gradient in psi/ft

Specific Gravity (SG) =pressure gradient in psi/ft ÷ 0.433

**Example: **

Pressure gradient = 0.50 psi/ft

Specific Gravity (SG) = 0.50 psi/ft ÷ 0.433

Specific Gravity (SG) = 1.15

## 3. Calculate specific gravity using mud weight in lb/ft^{3}

Specific Gravity (SG) = mud weight in lb/ft^{3}÷ 62.4

**Example:**

Mud weight = 90 lb/ft^{3}

Specific Gravity (SG)= 90 lb/ft^{3}÷ 62.4

Specific Gravity (SG) = 1.44

**Calculate Specific Gravity from Mud Weight In Metric Unit**

## 4. Calculate specific gravity using mud weight in kg/m^{3}

Specific Gravity (SG) = mud weight in kg/m^{3}÷ 1000

**Example: **

Mud density = 1200 kg/m^{3}

Specific Gravity (SG) = 1200 kg/m^{3}÷ 1000

Specific Gravity (SG)= 1.2

## 5. Calculate specific gravity using mud weight in g/cc

Specific Gravity (SG) = mud weight in g/cc÷ 1.0

**Example: **

Mud density = 1.2 g/cc

Specific Gravity (SG) = 1.2 g/cc÷ 1000

Specific Gravity (SG)= 1.2

## 6. Calculate specific gravity using pressure gradient in kPa/m

Specific Gravity (SG) = pressure gradient in kPa/m ÷ 9.81

**Example: **

Pressure gradient = 10 kPa/m

Specific Gravity (SG) = 10 kPa/m÷ 9.81

Specific Gravity (SG)= 1.02

**Please also find the Excel sheet for this topic – **Specific Gravity Calculation Sheet

**Ref books: **

Lapeyrouse, N.J., 2002. Formulas and calculations for drilling, production and workover, Boston: Gulf Professional publishing.

Bourgoyne, A.J.T., Chenevert , M.E. & Millheim, K.K., 1986. SPE Textbook Series, Volume 2: Applied Drilling Engineering, Society of Petroleum Engineers.

Mitchell, R.F., Miska, S. & Aadny, B.S., 2011. Fundamentals of drilling engineering, Richardson, TX: Society of Petroleum Engineers.