To realize nanomechanical graphene-based pressure and gas sensors, it is beneficial to have a method to electrically readout the static displacement of a suspended graphene membrane. Capacitive readout, typical in micro-electro-mechanical systems (MEMS), gets increasingly challenging as one starts shrinking the dimensions of these devices, since the expected responsivity of such devices is below 0.1 aF/Pa. To overcome the challenges of detecting small capacitance changes, we design an electrical readout device fabricated on top of an insulating quartz substrate, maximizing the contribution of the suspended membrane to the total capacitance of the device. The capacitance of the drum is further increased by reducing the gap size to 110 nm. Using external pressure load, we demonstrate successful detection of capacitance changes of a single graphene drum down to 50 aF, and pressure differences down to 25 mbar.Nanomechanical devices from suspended graphene and other two-dimensional materials have been receiving growing interest in the past few years for their potential as sensitive pressure 1-5 and gas 6-8 sensors. To realize integrated, small and low-power devices, it is necessary to have all-electrical on-chip transduction schemes, in contrast to the currently often employed laser interferometry techniques for the readout of their dynamic motion and static deflection.Reports on electrical readout of graphene membrane nanomechanical devices have employed readout schemes based on electrical transconductance 5,9 and piezoresistivity 1,3 . Both of these rely on the change in the conductance of the membrane as a function of deflection, which is then used to sense the motion of the membrane. Although these methods can be very sensitive, the graphene conductance can also be affected by variations in gas composition, humidity, light intensity and temperature. Moreover, the conductance is not only related to the deflection of the graphene membrane, but depends also on material parameters like the electron mobility and piezoresistive coefficients. These approaches therefore require calibration and a high degree of stability of the graphene and insensitivity to variations in its surroundings.In contrast, the capacitance between a graphene membrane and a bottom electrode is, to first order, a function only of the geometry of the system and, therefore, the deflection of the membrane. A measurement of the capacitance of the membrane can therefore be used to calculate its deflection, which makes capacitance detection an interesting alternative method for electrical readout of nanomechanical graphene sensors. Dynamic (onresonance) capacitive readout has been demonstrated on suspended graphene bridges 10,11 . Measurements using static capacitive readout of the deflection of graphene membranes have been conducted on a voltage tunable capacitor array comprised of thousands of graphene membranes in parallel 12 .Here we extend on this work by capacitive detection of the deflection of a single graphene drum and demon-A 3D schematic of t...