In Air Conditioning a "ton" = 12000BTU of heat removal per hour.

It originates from the amount of heat removal over a period of 24 hours needed to freeze a ton of water at 0C:

https://en.m.wikipedia.org/wiki/Ton_of_refrigeration

A quick idea of what cooling/heating you need is your square footage (assuming 8ft ceilings) x 20.

So 600 sq ft of area would need a 1 ton AC or 12,000BTU. Again complicated by outdoor temperature, insulation of the home, and other factors.

Anyway, what the op was saying, for the same tonnage (cooling capacity) old ACs used a ton of electricity. Newer split units are crazy efficient.

Like in 2000 the new requirement for a home AC was a SEER (cooling vs electric usage) of 10. The higher the rating, the less electricity used for a given cooling capacity.

Nowadays you can get the cheaper split units which have ratings of 19-23 SEER2. So they use half or less than half the electricity for the same cooling. Also they can work as heaters in a pinch.

Edit: Quick googling shows that ACs from the 80s could be as inefficient as 6-7 SEER. So a modern 21 SEER2 unit would use 1/3rd the electricity!