Blazars make up the largest fraction of Fermi-LAT-detected sources of high-energy gamma-ray emission. At the same time, their emission is known to be highly variable throughout the electromagnetic spectrum. With hints of their highest fractional variability in the radio regime being present at the highest radio frequencies, monitoring blazars at millimetre wavelengths will be one of the key science programmes of the Africa Millimetre Telescope (AMT).

Against this background, we study the expected science performance of the AMT based on a sample of 324 gamma-ray blazars with well-modelled spectral energy distributions, comparing three likely telescope sizes as well as the two possible locations.

We find that at 86 GHz, the performance of the AMT will not differ strongly amongst the telescope size and site options, while at 230 GHz and 345 GHz, a 13 m telescope will require 1.5 times the observation time of a 15 m telescope. A telescope close to the H.E.S.S. site will require 3 times (at 230 GHz) and 20 times (at 345 GHz) the observation time compared to a telescope on top of Mt. Gamsberg.