I would still be more comfortable converting tons to studs, rather than inches.
It is necessarily the weapons weight/size that determines its strength. The 100ton laser does more damage because it's bigger. The 100ton missile travels better because it is more engine and fuel. So while you say it is not weight, but size, you are missing that both are inherently tied together.
Converting tons to studs then just means that you do more damage with bigger built guns.