I am using the following raster calculation to create a topogrpahic wetness index in QGIS.

TWI/CTI = ln(a / (tan (beta))


a=Upland contributing area: [(flow accumulation + 1 ) * (cellsize)]
beta=slope in radians.

I have calcualted the slope and upland contributing area successfully. However, I don't know the cell size of my DEM. I am fairly new to GIS, so this is likely a dumb question, but how do I find the cell size of my DEM? I downloaded it from a government website. It is the Canadian Digitial Elevation model (https://open.canada.ca/data/en/dataset/7f245e4d-76c2-4caa-951a-45d1d2051333?activity_id=b9b143a0-447d-4a1d-9f13-8d5f4dc0fa33)

1 Answer 1


Open Properties of your raster layer (context menu: right click on the raster layer in the layer panel). In the Information tab, you find all the information - see screenshot 2 below.

To change pixel size, you can use Raster alignement or simply export the raster and change the resolution (and the CRS, if need be):

Screenshot 1, export dialog window: enter image description here

Screenshot 2, layer properties, indicating pixel size: enter image description here

  • Thank you. I have found the pixel size. However, is there a way to convert this to a single cell size value for the calculation above?
    – ryoung
    Dec 11, 2021 at 21:48
  • See updated answer
    – Babel
    Dec 11, 2021 at 21:52

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