How to calculate PPP$from LCUs? Is there one single formula which allows to calculate the income of a person in PPP\$ from her income in LCUs (local currency units), given for example the PPP conversion factor, GDP (LCU per international $) as published by the World Bank. Assume for example an Indian farmer with a monthly income of ₹50,000, given India's PPP conversion factor of 18 and exchange rate ₹70 =$1. What is his monthly income in PPP\$and by which formula? Is other or further information needed? Vice versa: What is the farmer's monthly income in rupees when his income is known to be PPP\$30?

References:

• Divide ₹50,000 by 70 to get about US$714 / month at market exchange rates • Divide ₹50,000 by 18 to get about PPP$2778 / month at PPP rates (so not a poor farmer)
• Multiply USD$30 by 70 to get ₹2100 at market exchange rates • Multiply PPP$30 by 18 to get ₹540 at PPP rates
• Nevertheless, this doesn't work: According to Gapminder's Dollar Street, PPP$30 is a somehow not atypical income of poor farmers, but ₹540 per month is an unrealistically low income: not even the poorest farmers earn only such a small amount per month. – Hans-Peter Stricker Oct 24 '19 at 20:47 • @Hans-PeterStricker Let's take the first example I came across from Gapminder of a fruit collector and family in West Bengal with a monthly income of PPP$29 per adult so presumably about ₹520. Now take the second case I found of a farmer and family near Chennai with a monthly income of PPP\$245 per adult so say about ₹4400 a month. Looking around their homes suggests different farmers can have very different incomes. – Henry Oct 24 '19 at 23:16