Is there an index, parameter, ecuation, or anything to compare the tax pressure exercised by a country in relation to others countries? In my country we are told often that the tax pressure over the companies and people is huge, making it unbearable and being a reason bankrupting the Economy, and one of the largests in the world. We are told that each product price is more than 50% of taxes and each company has to pay more than 50% in taxes for each employee they have. But when I take a look at the overall amount of money collected by taxes in a year, this seems to be over 100 times smaller than United States, a supposed very capitalist country which opposes heavy taxation. Of course we have to take in consideration other parameters, such how large are the economies of each country, but if I compare the amount of money collected with taxes in relation with the GDP of each country, it would seem my country pays half of the taxes of United States (100 times less taxes with 50 times less GDP than US) . I thought that may be I should compare people's wages with the amount of taxes divided the amount of people, but it still seems that United States is paying over twice the taxes that we pay here. 

Then, because of all of this, my question is, 

Is there an index, parameter, ecuation, or anything to compare the tax pressure exercised by a country to its own Economy in relation to the pressure exercised by others countries?
I am not sure how you calculated the tax revenue in relation to GDP, but one measure would be tax revenue as % of GDP. This is quite common measure of how heavy the taxation is because it tells you what percentage of total output produced by country is collected by government. OECD provides data on this measure here. 

However, it can always happen that even a country with high tax rate collects less taxes than country with lower tax rate. First, you have classic Laffer curve - if you set taxes to 100% you collect zero tax revenue because nobody will work for fee so you collect the same tax as at 0 tax rate - hence having higher tax rates does not necessarily mean higher tax revenue. This being said empirically most real life countries don’t have taxes so high as to be over the peak of the Laffer curve so this will probably not apply to your case. Another, issue is tax avoidance. In some countries it’s child’s play to avoid VAT or many people can work in informal sector to avoid income tax. If government does not have good institutions that prevent this then again even government with 50% tax rate can collect less tax revenue than government with 10% tax rate if in second country tax authorities are efficient in preventing tax avoidance but in first country not. 

Another possible measure could be looking at average or marginal tax rate across the economy and compare these between two countries. However, this is just crude comparison of how high taxes are.

If you would care about comparing the burdens the tax systems in the two countries create then a good measure is the marginal cost of public funds or marginal excess burden of taxation. This is a measure of by how much government must reduce economic activity (by its distortionary taxes) to extract 1 euro (or local currency). For example marginal marginal excess burden of  0.5 would imply that to raise 1e in tax revenue output on margin contracts by additional 0.5e so in total government has to take “out” of the economy 1.5e to get 1e. This gives you some idea of distortionary effect of taxes (in case of no distortions the marginal excess burden should be 0e). 

You can also calculate average excess burden which is the same measure but it gives you information about average burden instead of burden at the margin (i.e. the last euro collected). I don’t know of any dataset that just gives you this measure though because it has to be estimated and based on different estimation techniques or assumptions behind the model used you can get little bit different values, but you can try to search for it in google scholar. For US there are many papers trying to estimate the excess burden of almost any tax you can think of, but if you come from small country research might be not available on this.