Zakat is due on the current value of all assets (including gold), therefore the weight of gold and it’s current price must be known. Please keep in mind that items of personal use are exempt from zakat.
The obligatory zakat is first and foremost the right of the state. If you owe more zakat than what the state takes from you, then you have to look for people in your relatives, friends, acquaintances etc. that need help. If you still have zakat left over then you can spend it in other good causes of your choice. The tax that you pay to the state can be deducted from your total zakat obligation.
Please know that in addition to 2.5% zakat on assets, we are also obligated to pay zakat on production. This can be 5% or 10%. In Ghamidi sahab’s understanding, salaries, business income, service fees, etc. are all considered production. Please see the relevant chapter in Ghamidi sahab’s book Meezan for details.
Also please keep in mind that in addition to the obligatory zakat, we’re required to give in any good causes and needs of the society if we have money beyond our reasonable present and future needs.