You may need to calculate specific gravity from different density or pressure gradient units. This post demonstrates you about specific gravity calculation and specific gravity formulas frequently used in oilfield business.

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

Specific gravity formula : **Specific Gravity (SG) = mud weight in ppg ÷ 8.33**

**Example: **

Fluid = 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 formula : **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 formula : **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

Please also find the Excel Sheet: 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.