"Level" is often used loosely, as in "What is your level of uncertainty?" I would bet the price of a beer that the OP cares about how much fuel there is, not about physical height.
Weight is linear with amount, and therefore a useful (though a bit difficult to measure). If head is wanted, then pressure is the better on both counts -- ease of measurement, and direct linearity.
If height above the floor is wanted, then pressure is linear (with an offset that depends on the position of the gauge).
There are many options. The OP asked for practical help.
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Jerry