What is normal dose for losartan?

Losartan is a prescription medication only. Your Dr., when he/she prescribed this medication did not start your treatment by giving you the information on what dose you should be on?
Losartan treats HBP (hypertension) and also kidney damage for people with diabetes type II who have HBP as well.
So, I am not trying to be smart... about it, but self medicating a prescription drug such as Losartan is delicate, there are potential risks and possible side effects involved and you should see a Dr. in order to be evaluated to see if this is the right medication for you or NOT.

I will answer your question , but you MUST see a Dr. before you start self medicating.

Usual Adult Dose for Diabetic Nephropathy
Initial dose: 50 mg orally once a day
Maximum dose: 100 mg orally once a day

Comments:
-If hypertensive patients with left ventricular hypertrophy or type 2 diabetic nephropathy patients require titration from initial dose, increase to 100 mg orally once a day.
-Antihypertension is substantially present within 1 week but in some studies the maximal effect occurred in 3 to 6 weeks.

Uses:
-Treatment of hypertension.
-To reduce the risk of stroke in patients with hypertension and left ventricular hypertrophy.
-Treatment of diabetic nephropathy with an elevated serum creatinine and proteinuria (urinary albumin to creatinine ratio 300 mg/g or greater) in patients with type 2 diabetes and a history of hypertension.

Usual Adult Dose for Hypertension
Initial dose: 50 mg orally once a day
Maximum dose: 100 mg orally once a day

Comments:
-If hypertensive patients with left ventricular hypertrophy or type 2 diabetic nephropathy patients require titration from initial dose, increase to 100 mg orally once a day.
-Antihypertension is substantially present within 1 week but in some studies the maximal effect occurred in 3 to 6 weeks.

Uses:
-Treatment of hypertension.
-To reduce the risk of stroke in patients with hypertension and left ventricular hypertrophy.
-Treatment of diabetic nephropathy with an elevated serum creatinine and proteinuria (urinary albumin to creatinine ratio 300 mg/g or greater) in patients with type 2 diabetes and a history of hypertension.

Source: https://www.drugs.com/dosage/losartan.html