Several thousand tons cus he's stronger than Jonathan who is stronger than Tarkus who could do this https://vsbattles.fandom.com/wiki/User_blog:Chariot190/JoJo_Tarkus_lifts_a_%22small_mountain%22#articleComments with an assumption that this using only a tenth of his strength as one finger prolly accounts for 10% of his power. So we can say that Joseph compares to Jonathan who can at the very least lift 20527.02 tons or about the weight of a 60m long ship, pretty impressive

JoJo Tarkus lifts a "small mountain"VS Battles Wiki