What do your entered values produce?
Which rounding happens first?
An invented transaction weighing 561 units has virtual size ceiling(561 / 4) = 141 vbytes. Enter 141 in the size field. At an illustrative 2.125 sat/vB, multiplication gives 299.625 satoshis. A whole-satoshi target rounded up is 300 satoshis. The rate is an example, not a suggested payment rate.
Compare weight 560, which converts to 140 vbytes. At the same 2.125 sat/vB, the unrounded target is 297.5 satoshis and the rounded target is 298. Rounding down either stage could leave a lower effective fee rate than the target you intended.
How do weight and money differ?
Weight is base size × 3 + total serialized size. Virtual size is ceiling(weight / 4). These measurements describe transaction structure. Satoshis describe value. Equal payment amounts can have unequal virtual sizes when their inputs or scripts differ.
The actual fee in a transaction is the resolved input sum minus the output sum. This tool calculates a target from the size you enter. It does not inspect transaction bytes, estimate signatures or prove that a finished payment actually pays that target.
What does this calculator leave to you?
The converter accepts zero weight as an arithmetic boundary; the fee size must be positive. Fee rates may have at most three decimal places. Negative, exponential and nonnumeric entries receive an error instead of an apparently valid result. These input bounds keep the arithmetic exact within safe integer limits.
A calculated fee cannot promise relay or inclusion. Dependencies, local policy and miner selection still matter. Once loaded, this calculator’s logic works without a connection. Site analytics and the learning form are separate integrations and may still make requests while you are online.
Which specification defines these units?
Sources: Weight and virtual size definition; Transaction fee accounting. All selected amounts and fee rates in these tools are invented examples, not network observations.