Systems and methods of measuring beam current in a multi-beam apparatus are disclosed. The multi-beam apparatus may include a charged-particle source configured to generate a primary charged-particle beam, and an aperture array. The aperture array may comprise a plurality of apertures configured to form a plurality of beamlets from the primary charged-particle beam, and a detector including circuitry to detect a current of at least a portion of the primary charged-particle beam irradiating the aperture array. The method of measuring beam current may include irradiating the primary charged-particle beam on the aperture array and detecting an electric current of at least a portion of the primary charged-particle beam.