Transaction size model

Plan a Bitcoin transaction's inputs, outputs and fee

Model inputs, outputs, change and fee rates before you build a transaction. Nothing is signed, broadcast or linked to a wallet.

Build a transaction estimate

Enter the number and type of coins you plan to spend. The calculator estimates virtual size, then multiplies it by the chosen sat/vB fee rate.

InputsRecipient outputsInput typeFee rate (sat/vB) Include a change output

Estimated size -

Miner fee -

Fee in BTC -

Outputs created -

How fee rate changes this transaction

Hover the line to compare fee rates. The transaction shape stays fixed while the block-space bid changes.

UTXOs are the coins a transaction spends

A wallet balance is usually a set of unspent transaction outputs, or UTXOs. Spending three UTXOs generally needs three inputs, even when they belong to one wallet. More inputs mean more transaction data and usually a higher miner fee.

Change is a new coin

If selected inputs are worth more than the payment and fee, the wallet normally sends the remainder to a fresh change address. That change becomes another UTXO. Leaving change out does not make the remainder disappear: any unassigned value becomes miner fee.

Learn how this connects to Bitcoin transactions, inspect current demand in the mempool explorer, and compare quieter periods in the historical fee explorer.

Planning choices and their trade-offs

Choice	Possible benefit	Risk or cost
Consolidate many UTXOs	Fewer future inputs	Larger transaction now; may reduce privacy
Use native SegWit	Lower virtual size	Recipient software must support it
Avoid tiny change	Prevents uneconomic outputs	Coin selection must be handled carefully
Wait for lower fees	May reduce cost	No guarantee demand will fall

This is a size model

Multisig scripts, inscriptions, unusual witness data and wallet coin selection can change the real size. Confirm the final transaction in trusted wallet software before signing.

Method and boundary

What this planner estimates before a wallet takes over

The estimate is intentionally narrow: transaction shape multiplied by a chosen fee rate.

Size model

Input script type, input count, recipient outputs, and optional change produce an estimated virtual size.

Fee arithmetic

Estimated vbytes multiplied by sat/vB produces the satoshi fee. The amount being sent is not part of that multiplication.

Wallet remains authoritative

Coin selection, exact scripts, signatures, dust handling, and the signed transaction belong to trusted wallet software.

Transaction-planning questions that change the estimate

Does the amount of bitcoin set the fee?

No. Transaction weight and the sat/vB bid set the miner fee. A large payment with one modern input can be smaller than a tiny payment that combines many old outputs.

When is consolidation useful?

Consolidation can reduce future input count when block space is inexpensive. It can also join coins that were previously separate, which may reveal information about common ownership.

Why can my wallet show another size?

Wallets know the exact scripts, signatures and coin selection. This planner uses conservative standard-size assumptions, so the signed transaction remains the final source of truth.

Transaction size model

Know what a transaction weighs before you pay for it

The planner estimates size in virtual bytes from the number and type of inputs and outputs, then multiplies by a fee rate. Fees follow size, never the amount being sent, so the shape of a transaction is the cost.

Part 1
Inputs cost more than outputs
Each input carries a signature and a reference to the coin being spent; each output is only a value and a locking script. A wallet holding many small coins pays for every one of them each time it spends.
- Count inputs first: a legacy input is about 148 vB, native SegWit about 68 vB, Taproot about 57.5 vB.
- Outputs are 31–43 vB depending on address type, plus roughly 11 vB of fixed overhead.
- Consolidate small coins into one when the fee rate is low, not when you need to spend.
How Bitcoin fees are calculated →
Part 2
Choose a rate for the wait you can accept
Fee rate is quoted in satoshis per virtual byte. The mempool explorer shows the rates that recent blocks cleared; multiply the planner's size by that rate for a sat total, and by the current price for a fiat total.
- Next-block rates rise sharply during congestion.
- A payment that can wait a day often clears at a fraction of the next-block rate.
- Keep replace-by-fee enabled so an underpaid transaction can be raised.
Open the live mempool explorer →

Reference sheet

Typical sizes by input and output type

Component	Approximate size	Address prefix	Note
Legacy input (P2PKH)	148 vB	1…	Largest common input; full signature in the transaction body
Wrapped SegWit input (P2SH-P2WPKH)	91 vB	3…	Signature counted at a quarter weight
Native SegWit input (P2WPKH)	68 vB	bc1q…	Cheapest widely supported input
Taproot input (P2TR)	57.5 vB	bc1p…	Schnorr signature; smallest single-key input