# Buoyancy Factor

Published: July 21, 2017 | Last updated: July 5, 2023

## What Does Buoyancy Factor Mean?

The Buoyancy Factor is a calculation used to compensate for the apparent loss of weight of the parts of the drill string and bottom hole assembly due to being immersed in drilling fluid. The drill bit floats in the drilling mud, which changes its apparent weight in all HDD/trench calculations.This affects the operation of the horizontal/trenchless drilling equipment.

## Trenchlesspedia Explains Buoyancy Factor

If you stood on a scale at the bottom of a swimming pool, you would weigh less than if you weighed yourself on dry ground. That’s because you float when you’re in the pool’s water. The drill bit does the same thing, only it floats in the drilling mud.

To calculate the Buoyancy Factor, you must know

1. the mud weight in pounds per gallon or (ppg)
2. the mud weight in pounds per cubic feet (lb/ft3)

For example, if the mud weight in ppg were 50 lbs., the mud weight in buoyancy factor is calculated thusly:

BF = (65.5 – 50) ÷ 65.5

BF = 0.2366 in ppg

*65.5 = density of steel in ppg

(Note: 65.5 = pounds per gallon is the density of steel.)

BF = 489 – 50

BF= 439 lb/lb3

(Note: 489 is the density of steel)

Although reference cards are available, always use a calculator to perform this calculation and always perform it twice to ensure the correct answer.