Here is a thread about Ivermetin dosage here on BYC:
https://www.backyardchickens.com/threads/ivermectin-pour-on-dosage.727707/
And here is what Plumbs Veterinary Drug Manual says regarding Ivermectin dosage. Hope this helps.
Susceptible parasites (all are extra-label):
a)
Ascarids, Capillaria spp, and other intestinal worms; Knemidokoptes pilae (eg, scaly face and leg mites): Dilute ivermectin to a 2 mg/mL concentration. After diluting product, use immediately.
Most birds: 220 µg/kg IM60
Amazons: 0.1 mg IM
Macaws: 0.2 mg IM
Finches: 0.02 mg
b)
Ascarids, Coccidia spp, and other intestinal nematodes; Oxyspirura spp, gapeworms, Knemidokoptes pilae (eg, scaly face and leg mites): Dilute bovine preparation (10 mg/mL) 1:4 with propylene glycol to 1.25 mg/mL.
Most species: 200 µg/kg IM or orally, repeat in 10 to 14 days
Budgerigars: 12.5 µg (0.01 mL of diluted product- see above) IM or PO61
c) Ectoparasites: 200 µg/kg topically. Using 40 µg/mL spray (not available in United States), spray 1 pump per 200 g (0.44 lb) body weight.52,62,63 For routine prevention of common ectoparasites, this dose should be repeated monthly. For the treatment of an existing infestation, repeat doses are required 2 and 4 weeks after the initial application.