# Specific Gravity for Drilling

on . Posted in Drilling Engineering

Specific gravity, abbreviated as SG, a dimensionless number, is the density or ratio of any substance to another substance.  It sometimes may be called just gravity or relative density.  When calculating the specific gravity of a liquid or solid, water is normally the comparison (water has a specific gravity of 1).  Even though two objects are the same size, their density may be different.  The density of the substance and the density of water must be measured using the same units of mass and volume for accurate comparison.  This is expressed in how much more weight the object is in comparison to the same amount of water.  Likewise a gas is compared to air.

### Specific Gravity (Mud Weight $$\;lbm/gal$$) formula

$$SG = MW + 8.33$$     (Specific Gravity)

$$MW = SG - 8.33$$

Symbol English Metric
$$SG$$ = specific gravity $$dimensionless$$ -
$$MW$$ = mud weight (ppg) $$lbm\;/\;gal$$ -

### Specific Gravity (Pressure Gradient $$\;psi/ft$$) formula

$$SG = PG \;/\; 0.433$$     (Specific Gravity)

$$PG = SG \; 0.433$$

Symbol English Metric
$$SG$$ = specific gravity $$dimensionless$$ -
$$PG$$ = pressure gradient $$psi\;/\;ft$$ -

### Specific Gravity (Mud Weight $$\;lbf/ft^3$$) formula

$$SG = MW \;/\; 62.4$$     (Specific Gravity)

$$MW = SG \; 62.4$$

Symbol English Metric
$$SG$$ = specific gravity $$dimensionless$$ -
$$MW$$ = mud weight $$lbf\;/\;ft^3$$ -

### Convert Specific Gravity (Mud Weight $$\;lbm/gal$$) formula

$$MW = SG \; 8.33$$     (Convert Specific Gravity)

$$SG = MW \;/\; 8.33$$

Symbol English Metric
$$MW$$ = mud weight (ppg) $$lbm\;/\;gal$$ -
$$SG$$ = specific gravity $$dimensionless$$ -

### Convert Specific Gravity (Pressure Gradient $$\;psi/ft$$) formula

$$PG = SG \; 0.433$$     (Convert Specific Gravity)

$$SG = PG \;/\; 0.433$$

Symbol English Metric
$$PG$$ = pressure gradient $$psi\;/\;ft$$ -
$$SG$$ = specific gravity $$dimensionless$$ -

### Convert Specific Gravity (Mud Weight $$\;lbf/ft^3$$) formula

$$MW = SG \; 62.4$$     (Convert Specific Gravity)

$$SG = MW \;/\; 62.4$$

Symbol English Metric
$$MW$$ = mud weight $$lbf\;/\;ft^3$$ -
$$SG$$ = specific gravity $$dimensionless$$ -

Tags: Drilling