Is there any website, diagram or something that I could find that depicts how much a thing weighs, what that quantity looks like and how much calories it has?
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A website or diagram for ingredient amounts would have to be too exhaustive. Just take your items and measure them.
Your title asked about grams, which is a measurement of weight, so get a kitchen scale. If your recipe asks for milliliters, use a measuring cup. More often than not, you won't be able to just eyeball an amount, especially if baking a cake.
For calorie info, a quick search online will show databases of nutrition for various foods, but you'll have to measure ingredients to match up with their amounts. For example, 100 g of almond flour could have 144 calories, but you're baking with 250 g.
The short answer is to use some scales. However, from your question it seems likely that you don't have any to hand.
It depends on the density of the substance in question.
If the substance is mostly water (e.g. juice or milk), then you can approximate its density to be that of water, which means that you can get a good idea of its weight by measuring its volume. For example if you can measure 100 ml of it in a measuring jug, then you can be reasonably sure that weighs approximately 100 g.