Choose buoyancy factor or apparent weight, enter fluid and material densities, and select Calculate. Apparent weight also requires weight in air. Both modes use the entered material density.

Estimate static buoyancy for fully immersed material, or an open pipe filled with the same fluid inside and outside. This is not a complete hook-load or tension model.

ppg means pounds per US gallon. SG uses a 1,000 kg/m³ reference.

Default: steel, approximately 65.4 ppg. Prior preset estimates: stainless steel 66.8, aluminum 22.1, titanium 37.6 ppg. Enter the actual alloy density when known.

Related Calculators

Buoyancy Factor Formula

The following static formula gives the fraction of weight remaining for fully immersed material, or open pipe filled with the same fluid inside and outside. Air buoyancy is neglected; sealed or partly immersed objects require a different displacement model:

BF = 1 - (MW / MD)

Variables:

  • BF is the buoyancy factor (dimensionless)
  • MW is the mud weight (i.e., fluid density)
  • MD is the material density (i.e., object density)

To calculate the buoyancy factor, subtract the ratio of the mud weight (fluid density) to the material density (object density) from one. In common drilling practice for steel, a frequently used approximation is BF ≈ 1 − (MW / 65.4 ppg).

What is a Buoyancy Factor?

The buoyancy factor is a dimensionless number used to estimate the apparent (buoyant) weight of an object submerged in a fluid. In typical drilling usage, it is the multiplier that converts weight in air to apparent weight in the drilling fluid:

Weight in fluid = BF × weight in air

A lower buoyancy factor means a greater reduction in effective weight (more buoyant support). A buoyancy factor closer to 1 means less reduction.

How to Calculate Buoyancy Factor?

The following steps outline how to calculate the Buoyancy Factor:

  1. First, determine the mud weight (MW), i.e., the density of the fluid the object is submerged in.
  2. Next, determine the material density (MD) of the object (for example, steel is about 65.4 ppg).
  3. Use the formula BF = 1 – (MW / MD) to calculate the buoyancy factor.
  4. Finally, choose a mode, enter the densities and (for apparent weight) weight in air, then select Calculate. Steel defaults to approximately 65.4 ppg; use an actual alloy density when known. SG uses a 1,000 kg/m³ reference. This calculator supports fluid density from zero through the material density; equal densities give neutral buoyancy.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Mud weight (MW) = 12 ppg

Material density (MD) = 65.4 ppg (steel)

BF = 1 – (12 / 65.4) ≈ 0.8165