These are three simple lifting strength calcs to help determine Demon Slayer characters lifting strength.
Tanjiro pushing boulder[]
In Chapter 134 we see a boulder than Tanjiro eventually grows strong enough to push it through a town.
Tanjiro is 165 cm (1.65 m), which means that the diameter of the rock is 1.65 x (344/247) = 2.30 m
Assuming the boulder is a sphere for simplification, its volume would be 6.37 m^3
The average density of granite is between 2.65 and 2.75 g/cm^3, or about 2700 kg/m^3
The weight of the boulder is approximately: 6.37 x 2700 = 17199 kg [19 ton or Class 25 lifting strength]
Gyomei pushing larger boulder[]
Also from Chapter 134 we have Gyomei pushing a larger boulder.
Gyomei Himejima is an absolute unit with a height of 220 cm (2.2 m), which makes the diameter of the boulder (assumed to be spherical for simplification): 2.2 x (397/226) = 3.865 m
The volume of the sphere would then be 30.23 m^3
The average density of granite is between 2.65 and 2.75 g/cm^3, or about 2700 kg/m^3
The weight of the boulder is approximately: 30.23 x 2700 = 81621 kg [90 ton or Class 100 lifting strength]
Kyojuro lifting train by dashing[]
In Chapter 60 Kyojuro Rengoku casually performs what is likely the best lifting feat in the series.
Kyojuro wakes up in one of the back passenger cars in the train, and by dashing he caused the car Tanjiro is in to tilt forward, indicating that Rengoku caused significant lift in the entirety of the train by dashing.
The movie depiction (which is done with author supervision and involvement) indeed shows the entirety of the train lifting.
According to this source, wooden train passenger cars in early 20th century had a weight between 15 ton and 20 ton.
The train has eight cars, which means that the weight of the train is: 8 x 15 = 120 ton [108862 kg or Class K lifting strength]
It is of note that there is a Hashira arm-wrestling ranking which helps us determine lifting strength, and that strength alone does not determine AP as Shinobu and Obanai are weaker than Tanjiro in pure strength but are able to deliver very powerful stabs and slashes through technique.