How shop goods were weighed and measured before the mid 20th Century
At the time of my mother's childhood recollections of the early 1900s, relatively few goods came ready packaged from manufacturers. Shopkeepers weighed or measured out their goods themselves.
How shopkeepers sold their goods
Goods were sold by weight, volume, length, or per item, depending on what they were. Foodstuffs were generally sold by weight, measured in pounds (written as lbs) where 1 lb = 0.453592 kg. Larger units were used for heavy items like coal (which was delivered to the door), and smaller units were used for lightweight items like the powders dispensed by chemists.
To speed up sales the shopkeepers weighed out frequently requested goods into bags while the shop was closed using scales which worked by balancing the goods against known weights or on spring scales which worked by compressing a spring which moved a dial. There were a number of different types of scales based on balancing goods against weights, and also different types and ranges of weights, all shown on the scales page.
Commonly used weights in the early 1900s:
16 drams = 1 ounce (oz)
16 ounces (oz) = 1 pound (lb)
14 pounds = 1 stone (not abbreviated)
112 pounds = 1 hundredweight (cwt)
20 hundredweights = 1 ton
2240 pounds = 1 ton
This system of weights was known as the Imperial system.
There were always, though, customers who needed goods weighed out to order while they waited. Consequently waiting around and queuing to be served was a normal part of shopping. No-one seemed to mind. The women - as it was invariably women who did the shopping - knew nothing else, and it gave them the opportunity to indulge in social chit-chat without feeling guilty that they ought to be at home doing housework.