TL;DR
Each coin you spend from a 2-of-3 multisig carries two signatures and a small script, so it takes more block space than a single-sig coin. Expect about half as much again per input, or roughly a third more for a typical whole transaction. For savings you rarely move, that’s a small price.
Where the extra size comes from
Spending a single-sig coin needs one signature and one public key. Spending from a 2-of-3 needs two signatures plus the script listing all three public keys. Thanks to SegWit, that extra data counts at a discount, which keeps the difference modest.
| Per input, approximately | Single-sig (P2WPKH) | 2-of-3 multisig (P2WSH) |
|---|---|---|
| Size in virtual bytes | about 68 | about 104 |
| At 10 sats per virtual byte | about 680 sats | about 1,040 sats |
| At 50 sats per virtual byte | about 3,400 sats | about 5,200 sats |
A sat is one hundred-millionth of a bitcoin; a virtual byte is the unit block space is measured in. The whole transaction also has fixed parts and outputs, so the total difference is smaller than per input. Figures are rounded.
How to keep fees down
- Receive in larger chunks rather than many small payments: each coin is one input when you spend.
- Move coins when the network is quiet; Sparrow’s fee slider shows the current state.
- Don’t pay for High Priority when Low Priority is fine for savings.
- Stuck anyway? Raise the fee with RBF.
Worth it?
For savings you touch a few times a year, a few hundred to a few thousand extra sats per transaction is little compared to what multisig protects. For daily spending, use a single-sig wallet. More in multisig vs single-sig.