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Since blockchain is public.. can it be found how many bitcoin you own by having your bitcoin public address?

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Yes. Simply paste your bitcoin adress into a block explorer such as http://blockchain.info

For example, this adress has 200$ pending -> https://blockchain.info/address/1Lx4aebbGAUA2ASuYBoiAC2akutzpZQMzb Or, 0.025631 BTC

You can also add a watch-only adress in bitcoin-core / electrum to keep track of balances from certain adresses.

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A typical bitcoin wallet consists of many different individual addresses, and does not have a unique ID that can be queried.

So while it is quite easy to learn how much BTC any single address has, learning how much BTC an individual user has, with any certainty, is extremely difficult.

If you want to know your own balance, your wallet-software should tell you that quite easily.
If you want to learn the balance of another user, that is difficult.

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