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Web3 tools
Bitcoin Transaction Size Calculator
Estimate the virtual size of a Bitcoin transaction from its inputs and outputs, and price it at the live mempool fee rate. Size is what actually drives a Bitcoin fee, so the script type you spend from matters more than the amount you send.
What you are spending. This drives most of the size.
Each previous payment you are spending is one input.
Where the coins are going.
Recipients plus a change output, if there is one.
Size breakdown
This transaction is 372 bytes on the wire but you only pay for 209 vB. Witness data counts a quarter as much as the rest, which is the whole reason SegWit inputs are cheaper to spend.
Against the same transaction built entirely from legacy inputs you save 159 vB (43%).
What the input type is worth
The same 2-in 2-out transaction at 6 sat/vB, priced with each input type.
| Input type | vBytes | Fee | vs legacy |
|---|---|---|---|
| Legacy | 368 | 2,208 sats | — |
| Nested SegWit | 255 | 1,530 sats | -31% |
| Native SegWit | 209 | 1,254 sats | -43% |
| Taproot | 188 | 1,128 sats | -49% |
Size by script type
Approximate virtual size contributed by a single input or output of each type. Inputs dominate because they carry signatures.
| Type | Address starts with | Input vB | Output vB |
|---|---|---|---|
| Legacy (P2PKH) | 1 | 148 | 34 |
| Wrapped SegWit (P2SH-P2WPKH) | 3 | 91 | 32 |
| Native SegWit (P2WPKH) | bc1q | 68 | 31 |
| Taproot (P2TR) | bc1p | 58 | 43 |
Note the trade-off in the last row: a Taproot input is the cheapest to spend, but a Taproot output is the largest to create. Paying to a Taproot address costs slightly more today and saves more later.
Related tools
- Gas Fee Estimator — the EVM equivalent, where fees are priced in gas rather than size.
- Wallet Address Checker — confirm which script type an address actually is.
- Mining Profit Calculator — the other side of the fee: what miners earn from them.
Frequently asked questions
What is a vByte?
A virtual byte is the unit Bitcoin fees are actually charged in. Since SegWit, a transaction has a weight in weight units and the virtual size is that weight divided by four. Witness data counts a quarter as much as the rest, so it is cheaper.
Why does the number of inputs matter so much?
Each input carries its own signature, so it adds far more size than an output does. A P2WPKH input is about 68 vB against 31 vB for an output, which is why consolidating many small payments is expensive.
Are these sizes exact?
They are accurate estimates. ECDSA signatures vary by a byte or so depending on the values, so a real transaction can differ very slightly. Taproot key-path spends use fixed 64-byte Schnorr signatures and are exact.
Which address type is cheapest?
Taproot inputs are the smallest, then native SegWit, then wrapped SegWit, with legacy the most expensive. Switching from legacy to native SegWit typically cuts the size of a spend by roughly 25 to 30 percent.
Does this work for Ethereum?
No. Ethereum fees are priced by gas, not by transaction size. For EVM chains use the gas fee estimator instead, which covers 50 networks.