Mud balance, also known as a mud scale is a device used to measure the density (weight) of drilling fluid, cement or any type of liquid or slurry.

It consists of a graduated beam with a bubble level and a weight slider along its length and a cup with a lid on one end. The cup is used to hold a fixed amount of fluid so it can be weighed. A slider-weight can be moved along the beam, and a bubble indicates when the beam is level. Density is read at the point where the slider-weight sits on the beam at level.

Calibration is done using a liquid of known density (often water) by adjusting the counter weight. Typical balances are not pressurized, but a pressurized mud balance operates in the same manner. It’s a device to measure density (weight) of mud, cement or other liquid or slurry. A mud balance consists of a fixed-volume mud cup with a lid on one end of a graduated beam and a counterweight on the other end. A slider-weight can be moved along the beam, and a bubble indicates when the beam is level. Density is read at the point where the slider-weight sits on the beam at level. Accuracy of mud weight should be within +/- 0.1 lbm / gal (+/- 0.01 g / cm3). A mud balance can calibrated with water or other liquid of known density by adjusting the counter weight. Most balances are not pressurized, but a pressurized mud balance operates in the same manner.