Slc to grd

Notice that the IW GRD product has a pixel size 10 * 10m with multilook 5 * 1.
I am trying to reproduce the GRD product from SLC using the snap slc to grd function. But with 5 * 1, the pixel size is around 16 * 16m, I am wondering how they get the final 10 * 10m result.