Luminosity calibration at ATLAS in 2011

An overview is provided of absolute luminosity calibrations of dedicated luminosity detectors and algorithms at ATLAS for different LHC physics conditions. Emphasis is placed on their precision calibration in ts=7TeV proton-proton collisions. Details of systematic uncertainties associated both with this calibration and its subsequent application to typical running conditions in 2011 are presented. A preliminary estimate of the total uncertainty is shown to approach a precision of $sim$2%. Potential correlation of this uncertainty with that expected in 2012 proton-proton collision data is discussed.