The table below shows approximate values of the buoyancy corrections needed when comparing stainless steel weights with those of other materials, in air of density 1.2 kg/m³ and on a true mass basis.

Buoyancy corrections applicable when comparing the true masses of dissimilar materials in air.

(*) This buoyancy correction would be necessary when comparing two stainless steel weights, one with a density of 7 800 kg/m³ and the other with a density of 8 200 kg/m³.

The table illustrates that, even when comparing weights of nominally the same material (such as stainless steel), attention must be paid to buoyancy effects when good measurement uncertainties are required. When comparing weights of dissimilar materials the effect of air buoyancy becomes more significant and must be applied even for routine calibrations when true mass values are being determined.

When working on the basis of conventional mass the buoyancy corrections become smaller than those applicable to true mass. OIML recommendation R 33 uses air densities ranging from 1.1 kg/m³ to 1.3 kg/m³ (ie approximately ±10% of standard air density) and this range yields buoyancy correction limits that are only about one tenth the value of the corresponding true mass buoyancy corrections. When the limits specified by OIML R 33 for the density of weights in Classes E₁ to M₃ are taken into account too, the maximum correction for any weight is one quarter of its tolerance. This is generally not significant for weights of Class F₁ and below - although allowance should still be made in the uncertainty budget for not applying the correction. For Class E₁ and E₂ weights, however, buoyancy corrections need to be applied in order to achieve the values of uncertainty demanded of these Classes.