The larger the canister, the higher the ratio of gas to container weight. The canister on the pic should be around 15kg of gas. Based on other similar canisters, the canister should weigh around 40kg when full. That makes the weight ratio about 3:5.

But for smaller canisters, for example this 1.5kg canister, the weight ratio drops to about 3:7.

You should still be able to easily tell the difference between empty and full, I was just interested in the gas to container weight ratios