Bitcoin fees: sat/vB versus total sats
Convert a fee rate and transaction virtual size into total satoshis, BTC and an optional dollar estimate.
Total fee in sats = virtual size in vB × fee rate in sat/vB
Fee in BTC = total sats / 100,000,000A hypothetical fee estimate
A transaction estimated at 140 vB with a rate of 8 sat/vB costs 1,120 sats, or 0.0000112 BTC. At an example BTC price of $60,000, that is about $0.67. The BTC price changes the dollar conversion; it does not change the 1,120-sat fee.
| Virtual size | Rate | Total fee |
|---|---|---|
| 140 vB | 2 sat/vB | 280 sats |
| 140 vB | 8 sat/vB | 1,120 sats |
| 250 vB | 8 sat/vB | 2,000 sats |
Why two sends can have different sizes
Transaction size depends on its inputs, outputs and spending format. A wallet balance assembled from many small unspent outputs can need more inputs when spent. The amount sent alone is not enough to determine virtual size. Use your wallet’s transaction preview or a decoded transaction instead of assuming that every transfer has the same size.
Read a recommendation as an estimate
The fee tool can load a stored mempool.space recommendation, showing its source time. Recommendations reflect observed network conditions and a target urgency. They do not reserve block space or guarantee a confirmation deadline. If the source is stale or unavailable, enter a rate manually and check your wallet before broadcasting.
- Use vB rather than raw serialized bytes for a sat/vB calculation.
- Check whether a wallet displays sat/vB, sats, BTC or a fiat total. These units are not interchangeable.
- An exchange withdrawal fee can be a fixed service charge and may differ from the transaction’s network fee.
- Keep an additional balance for the network fee when sending a chosen amount.
- Replace-by-fee and other fee changes depend on the transaction and wallet capabilities.
Use the final transaction for reconciliation
The estimate is useful before sending, but the broadcast transaction gives the final virtual size and total fee. Compare them with the preview if the final amount differs. Decimal rates can produce a fractional-satoshi estimate. A wallet uses whole satoshis and may round the final fee. Saving alternative rates lets you compare cost without creating or signing a transaction.
Why is the wallet estimate different?
Check whether the wallet uses the same fee rate and virtual size. Extra inputs, a change output or a different transaction format can change the size. A withdrawal charge set by an exchange is also a different input from an on-chain fee estimate.
Check the inputs before comparing results
- Copy virtual size from the wallet preview, not the amount being sent.
- Check the observation time beside a stored recommendation.
- After confirmation, compare the final size and fee with the estimate.
Use the related calculator to compare your own inputs. The result is an arithmetic estimate based on the assumptions above.