We present a high-speed, contrast free, quantitative ultrasound velocimetry (vUS) for blood flow velocity imaging of the whole coronal section of rodent brain, complementing the high-speed, non-quantitative functional ultrasound imaging (fUS) and the low-speed, quantitative velocimetry by ultrasound localization microscopy (vULM). We developed the theory for analyzing the normalized first order temporal autocorrelation function of ultrasound speckle dynamics to quantify 'angle-independent' blood flow velocity. Further, by utilizing an ULM spatial constraint on the bulk motion rejected data, vUS provides high resolution blood flow velocity images at a frame rate of 1 frame/s, compared to ~ 2 mins per frame with vULM. vUS was validated with numerical simulation, phantom experiments, and in vivo measurements against vULM. We demonstrated the functional imaging ability of vUS by monitoring blood flow velocity changes during whisker stimulation in awake mice.