How do we calculate the correct transaction fee to send?

[Febo]

Also, suppose the transaction is not urgent (say changing BTC between own wallets or sending to a relative), can it be sent with very low fee? What's the worse that can happen - will the transcation get cancelled/not go through on the blockchain?

Not directly related, but you mention not urgent transaction. I noticed that usually mempool gets fuller towards end of the week and empty over weekends. So cheapest day to send a transaction is Sunday. Or the fastest day to send cheap transaction.

You made me curious about transaction fee in different days of week.
I calculated the average transaction fee for different days of the week in the past three months. (Raw data from https://bitinfocharts.com/)

Monday: 0.70 $
Tuesday: 0.70 $
Wednesday: 0.71 $
Thursday: 0.71 $
Friday: 0.74 $
Saturday: 0.63 $
Sunday: 0.57 $

You were right. I hadn't ever noticed this.

LOL well I never went to check exact numbers but saw it just by looking at mempool graphs. And we of course usually look at mempool when is more full then usually   At those times difference is for sure bigger.

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[o_e_l_e_o]

At those times difference is for sure bigger.

A bigger contrast is seen at times of the day. Go to https://jochen-hoenicke.de/queue/#1,6m and zoom in (by selecting an area on the graph) on a random week or so in the last few months. Generally when you see a surge in the mempool size, and therefore the average fee, it is usually around 13:00 - 23:00 UTC, which corresponds to day time in most of Europe, and initially the east coast and then all of the Americas. Conversely, the mempool is usually fairly empty, with fees around 1-2 sat/byte, around 01:00 - 06:00 UTC, when the aforementioned continents are generally sleeping and Australia and eastern Asia are awake.

You can use this to your advantage to plan non-urgent transactions, such as consolidating all your small inputs.

[hd49728]

Generally when you see a surge in the mempool size, and therefore the average fee, it is usually around 13:00 - 23:00 UTC, which corresponds to day time in most of Europe, and initially the east coast and then all of the Americas. Conversely, the mempool is usually fairly empty, with fees around 1-2 sat/byte, around 01:00 - 06:00 UTC, when the aforementioned continents are generally sleeping and Australia and eastern Asia are awake.

Perfect! It means most of bitcoin transactions have been made in America and European continents and locals there tend to use higher fees (likely), whilst the Asia and Australia continents tend to make less numbers of transactions as well as they likely are ready to move their coins with lower fees.

[RapTarX]

Perfect! It means most of bitcoin transactions have been made in America and European continents and locals there tend to use higher fees (likely), whilst the Asia and Australia continents tend to make less numbers of transactions as well as they likely are ready to move their coins with lower fees.

It's not because some people pays higher fees or some pays lower. If someone needs faster confirmation, they are likley to pay higher fee. Since we have limited space on block (4MB per block now), if there are a lot of transaction pending, you are likely to pay the maximum fee for faster confirmation if you are in hurry because only limited number of transactions will get place in the block (~4MB). That's how fee increase and decrease. No one is likely to pay higher fee unless they need to.

[sovie]

I use electrum wallet and usually I drag the cursor to left to set lowest fee, then click preview and you can see how many bitcoins are being deducted as fee. I don't know about other wallets.

[o_e_l_e_o]

because only limited number of transactions will get place in the block (~4MB).

A block (at present) can never contain 4 MB worth of transactions.

The limit on a block at present is 4,000,000 weight units. See my reply on the previous page for a brief explanation of what weight units are. Legacy transactions are only non-witness data, so take up 4 weight units per byte, and a block could fit a maximum of 1 MB. Witness data takes up 1 weight unit per byte, so if a block contained nothing but witness data, it would be 4 MB.

There are no transactions which are just witness data, though. SegWit transactions contain both non-witness (at 4:1) and witness (at 1:1) data. A block filled with regular SegWit transactions and no legacy transactions has an upper limit of somewhere around 2.5 MB. The biggest block we've ever seen so far was block number 566575, at 2.377 MB.

[figmentofmyass]

because only limited number of transactions will get place in the block (~4MB).

A block (at present) can never contain 4 MB worth of transactions.

The limit on a block at present is 4,000,000 weight units. See my reply on the previous page for a brief explanation of what weight units are. Legacy transactions are only non-witness data, so take up 4 weight units per byte, and a block could fit a maximum of 1 MB. Witness data takes up 1 weight unit per byte, so if a block contained nothing but witness data, it would be 4 MB.

There are no transactions which are just witness data, though. SegWit transactions contain both non-witness (at 4:1) and witness (at 1:1) data. A block filled with regular SegWit transactions and no legacy transactions has an upper limit of somewhere around 2.5 MB. The biggest block we've ever seen so far was block number 566575, at 2.377 MB.

there are edge cases where we could theoretically get very close to 4MB. https://bitcoin.stackexchange.com/a/54949

The best possible size to weight ratio I can think of is a transaction which also spends a P2WSH output that has a ridiculous redeemscript. And then there's also the coinbase transaction and block header. The witness would be 4000000 - 240 * 3 - 240 = 3999040. So there is 3999040 bytes in the witness. The total block size is then 3999040 + 240 = 3999280 bytes.

in practice, miners would ignore such transactions unless they paid ridiculously high fees. so it doesn't happen.

[pooya87]

in practice, miners would ignore such transactions unless they paid ridiculously high fees. so it doesn't happen.

such transaction won't even be relayed as it would be non-standard so it doesn't exist in 99.9% of the node's mempool. the only way to see something like this is for a miner to both create this transaction and mine it in which case there is no need to pay any fees.

[figmentofmyass]

in practice, miners would ignore such transactions unless they paid ridiculously high fees. so it doesn't happen.

such transaction won't even be relayed as it would be non-standard so it doesn't exist in 99.9% of the node's mempool. the only way to see something like this is for a miner to both create this transaction and mine it in which case there is no need to pay any fees.

point taken, it wouldn't normally be relayed by nodes. however, that just means the spender needs to send the transaction to miners out-of-band.

[sima_sara]

isn't there a simple site where you can input few data and it gives you an estimated transfer fee?  I want to know how much it costs to transfer 10 Bitcoin from 1 wallet to another wallet.

[hosseinimr93]

isn't there a simple site where you can input few data and it gives you an estimated transfer fee?  I want to know how much it costs to transfer 10 Bitcoin from 1 wallet to another wallet.

Note that transaction fee doesn't depend on the amount you send. So, it doesn't matter whether you are sending 1000 BTC or 1000 satoshi.
When you make a transaction, you should set the fee rate according to network state and how fast you want your transaction to be confirmed. The total fee depends on number of inputs and outputs and address(es) type as well. You can use bitcoindata.science (a tool created by the forum user, bitmover) to calculate the total fee based on number of inputs and outputs, your address type and the fee rate.

[o_e_l_e_o]

isn't there a simple site where you can input few data and it gives you an estimated transfer fee?  I want to know how much it costs to transfer 10 Bitcoin from 1 wallet to another wallet.

Sites will generally give a suggested fee rate, rather than an absolute fee. The fee rate should be in the format of sats/vbyte. This is how much satoshi you will pay for each virtual byte of space your transaction takes up. The number of virtual bytes a transaction takes up is dependent on the number of inputs, the number of outputs, the exact type of those inputs and outputs (legacy, segwit, etc), and a few other factors.

For example, if your transaction was 2000 vbytes and you paid 1 sat/vbyte, you would pay 2000 sats. Your transaction would be right at the bottom of the current mempool, since miners care more about the fee rate than the absolute fee.
If your transaction was 250 vbytes and you paid 8 sats/vbyte, you would also pay 2000 sats, but this time your transaction would be much nearer the top of the current mempool.

A transaction moving 10 bitcoin could involve 1 input and 1 output and therefore be as low as 110 vbytes in size, or it could involve 100 inputs (or more) and be thousands of bytes in size. It all depends on across how many inputs that 10 bitcoin is spread.

[Eureka_07]

isn't there a simple site where you can input few data and it gives you an estimated transfer fee?  I want to know how much it costs to transfer 10 Bitcoin from 1 wallet to another wallet.

There are various wallets/exchanges that provides you the estimated or even the exact transaction fee, one example for the wallet is Mycelium. The transaction fee is based and calculated through the amount you have inputted, the priority of the transaction that you selected, and the current state of the mempool, particularly, the traffic.

[nc50lc]

There are various wallets/exchanges that provides you the estimated or even the exact transaction fee, one example for the wallet is Mycelium. The transaction fee is based and calculated through the amount you have inputted, the priority of the transaction that you selected, and the current state of the mempool, particularly, the traffic.

Users have previously mentioned that it's entirely not based from the amount.

If your comment is based from self-experience, it's most likely that you have multiple inputs with small amounts that it would take 2 or more inputs to fulfill the high amount you've inputted.

e.g.: Let's say you've received 0.0001, 0.00011 and 0.00012 BTC before that aren't consolidated into 1 UTXO.
If you need to send 0.00009 BTC; it will only have to use 1input, thus smaller transaction size and lower fee.
If you need to send 0.0003 BTC; it will have to use all three inputs, thus higher transaction size and higher fee.