<p>Fluid velocimetry is fundamental to a breadth of applications spanning academia and industry; however, velocimetry at high temporal resolution is often prohibitively costly. Here, we introduce a Fast and InExpensive Velocimeter (FIEVel) based on an optical mouse sensor. At its core, the optical mouse sensor consists of a small pixel array that acquires image data at high rates, with onboard hardware to compute and output motion in two orthogonal axes directly. We adapt this widely available integrated circuit to image illuminated particles in the bulk of a fluid as in standard particle image velocimetry (PIV). We demonstrate that FIEVel is capable of resolving two components of pointwise velocity (0d2c) nonintrusively in the bulk of a flowing fluid at rates up to 6.4 kHz, at orders of magnitude lower cost than traditional velocimetry devices. We demonstrate and validate the velocimeter across a range of flows, operating conditions, and illumination strategies. As a sample application, we measure the temporal spectrum of a grid-generated turbulent flow and show excellent agreement with traditional particle image velocimetry using a high-speed camera.</p>