Check out Projection in RealSense SDK 2.0 · IntelRealSense/librealsense Wiki · GitHub and the 'align' samples provided with the SDK.
If you align the depth frame before generating the point cloud, the point cloud will be aligned to the colour image so there is a 1:1 relationship between them.
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You can find some examples on how to retrieve the depth of a pixel in meters in the Depth Image Formats section: