The Full Form of MMWC is Millimetres water column.

Millimeters, water gauge, also known as a millimetre of water (US spelling millimeter of water) or millimetres water column and abbreviated to mmwg, mmH₂O or mmwc, respectively, is a less commonly used unit of pressure.

Millimeters of Water Column is a low range metric pressure unit derived from the hydrostatic pressure of 1mm head of water at 4 degC. 1 millimeter of water gauge equals 9.80665 pascals.

The mmH2O pressure unit is used for monitoring low air flow pressures used in building ventilation systems or very low water levels in rivers and streams. Historically low air pressures were measured using water column manometers but although these instruments have been mostly replaced by digital manometers which use electronic sensors, the mmH2O pressure unit remains in use.

A centimetre of water (US spelling centimeter of water) is a unit of pressure. It may be defined as the pressure exerted by a column of water of 1 cm in height at 4 °C (temperature of maximum density) at the standard acceleration of gravity, so that 1 cmH₂O (4°C) = 999.9720 kg/m³ × 9.80665 m/s² × 1 cm = 98.063754138 Pa ≈ 98.0638 Pa, but conventionally a nominal maximum water density of 1000 kg/m³ is used, giving 98.0665 Pa.

The centimetre of water unit is frequently used to measure the central venous pressure, the intracranial pressure while sampling cerebrospinal fluid, as well as determining pressures during mechanical ventilation or in water supply networks (then usually in metres water column). It is also a common unit of pressure in the speech sciences. This unit is commonly used to specify the pressure to which a CPAP machine is set after a polysomnogram.

1 cmH2O (conventional)	= 98.0665 pascals
	= 0.01 metre water (mH2O), metre water column (m wc) or metre water gauge (m wg)
	= 10 mm wg
	= 0.980665 mbar or hPa
	≈ 0.393700787401575 inH2O
	≈ 0.000967838 atm
	≈ 0.735559240069085 torr
	≈ 0.73555913527668 mm Hg
	≈ 0.0289590210738851 inHg
	≈ 0.0142233433071196 psi