scale_your_monitors_to_same_physical_size.py

import subprocess
data = subprocess.check_output('xrandr').decode('utf8').splitlines()
outputs = [x for x in data if x and x[0] not in 'S \t']

def parse_output(line):
    parts = line.split()
    name = parts[0]
    primary = 'primary' in parts
    w_in_mm, h_in_mm = [p.split('mm')[0] for p in parts if p.endswith('mm')]
    res_x, res_y = [p for p in parts if 'x' in p][0].split('+')[0].split('x')
    return(name, primary, int(res_x), int(res_y), int(w_in_mm), int(h_in_mm))

for o in outputs:
    name, primary, res_x, res_y, w_in_mm, h_in_mm = parse_output(o)
    if primary:
        prim_density_x = res_x / w_in_mm
        prim_density_y = res_y / h_in_mm
        break
    
print('xrandr ', end='')
for o in outputs:
    name, primary, res_x, res_y, w_in_mm, h_in_mm = parse_output(o)
    if primary:
        continue
    dens_x = res_x / w_in_mm
    dens_y = res_y / h_in_mm
    scale_x = prim_density_x / dens_x
    scale_y = prim_density_y / dens_y
    print(f'--output {name} --scale {scale_x}x{scale_y}')