Chalk it up to American Exceptionalism but I don't know if there are any countries other than the US that have not adopted the metric system. It feels archaic to be still using feet and pound, ounces and such not to talk of pints, quarts and gallon which let me point out is different from the imperial gallon. The scientific community like the rest of the world uses the metric system. The medical community prescribes dosage (cc's, milligrams, or grams) based on body weight in kilograms. But the general populace continues to use the old units and when it comes to tools, depends on conversion charts like the one in this article. Of course an adjustable wrench (or monkey spanner) works well for many applications.
Historically weights and measures along with balances have been used in India for a very long time going back to 2000 BC. Such artifacts have been discovered in Harappa and other sites of the Indus Valley Civilization. The ivory ruler found there may be the oldest such in the bronze age. There is a remarkable consistency in weights and linear measurements which indicate that they had a standardized system. If you are interested in details, just go to History of Measurement Systems in India. This page has an amazing chart of time measurement in India ranging from one ten millionth of a second to 22nd power of 10 years.
Growing up at a time when we were in the middle of adopting the metric system, I had to learn the different units that were prevalent then and the conversion rates among them. Like in everything else, units in India differed from place to place. I have heard my grandmother mention the local currency in the Travancore kingdom where she was raised. Luckily, the currency had been standardized across the nation by the time I was born. But as part of the drive to go metric, the currency was redesigned in 1957 to use 100 naya paise (new paise) per rupee from the older 192 paise per rupee along with other coins. For a few years the old coins continued to be in circulation until they were discontinued in 1964. I remember the old coins still especially the quarter anna which was annular shaped. We did not have the British currency and did not have to deal with tuppence and muppets or whatever they use over there.
With weights and other measures, we had to deal with the traditional measures such as tola, palam, seer, vis that were used for normal articles and specialized smaller measures for precious metals as well as the British ones along with the new metric units and the conversion rates among them. Depending on what you were measuring, either the British units (feet, furlongs, miles for distance) or the indigenous measures (for liquids and for weights) were in vogue.
While the metric system is easy to remember and use in calculations, our brains take time to adjust to the new measures. Even now we seem to be using feet and inches to denote height but for weight we seem to have moved to metric in India. Somehow to say you are 1.7 m tall seems odd. We were always trying to convert to the equivalent metric units or vice versa when transacting with shopkeepers. I think they in turn may have used the confusion to their advantage by quoting prices in as yet unfamiliar units.
Fruits were sold by numbers and price for them was quoted per dozen. I don't think that the dozen as a measure is Indian. It was probably introduced by the British although counting by twelve may have older origins in Mesopotamia. It is convenient to count up to twelve using the phalanges of the fingers on one hand. Twelve is also divisible by two, three, four and six making calculations easy. Nowadays you will find fruits being sold by weight in most places. It always gives me pause. For example, I know how many bananas I want to buy but not how much by weight. In this context, I must mention my recent experience with Instakart where we ordered two pounds of tomatoes but ended up just two tomatoes. The app too seems to have been confused! Or was it the shopper?
We also had (and still use) informal measures in use for some things. Flower vendors sold strands of jasmine and other flowers by arm length (muzham in Tamil). This would lead to some contention and haggling as the flowers may be strung densely or sparsely, not to mention the fact that the measure would vary from seller to seller depending on how tall or short they were. The price may very well be directly proportional to the density of flowers. This was the reason perhaps that in some places the practice is to sell jasmine strands by the count - you were quoted a price per one hundred flowers. In this case, they tended to be strung together densely. You could also buy loose flowers and string them yourself.
Standardization is obviously important in units of measurement. Informal units like the muzham may not matter much as the transactions are of low value but when dealing with land for instance they become critical. In this context, you will recall how King Bali was tricked by Lord Vishnu. Vishnu appeared as Vamana, the short one and asked for a little piece of land measured by just three paces. The moment Bali agreed to gift Him the land, He assumed His cosmic form and measured the earth and the heavens with just two paces. With no place for Him to place His foot for the third step, Bali offered the top of his head. Upon Vishnu placing His foot on his head, he was sent to the deepest nether world and is confined there even today appearing on earth only once a year during the Onam festival in Kerala. If only he had insisted on a standard measure!