In QGIS, I'm trying to create a vector grid layer with cells 150m x 150m, yet it only seems to be possible in degrees.
Is there a setting I need to change, or is there an equivalence I can use to convert degrees to meters?
You have to set your Project CRS to something using meters, like UTM or State plane. Then you can use
Vector -> Research Tools -> Vector Grid ... to create a grid in the same projection.
You should set the
X parameter to something useful, e.g. 150 for a 150m-grid.
Do you have a layer which you want to create the grid layer from? If so make a buffer around them. Use the extend of the bufferlayer to make the grid.
Oh and if not, then try this.
That should do it.