The signature line on a Solana receipt
When a transfer of SOL is confirmed, the receipt carries a fee that is easy to skip because it is small beside the amount sent. In the reading room we start with that line and we stay there until it is counted.
A signature on Solana is priced at a base of 5,000 lamports. One SOL is 1,000,000,000 lamports, so the base signature is 0.000005 SOL. If the transaction carries two signatures, the base fee is 10,000 lamports. The rule we write on the worksheet is plain: count the signatures, then multiply by 5,000.
Why the line is easy to misread
Visitors often arrive with the idea of a single network fee, one number that covers everything the chain did. The printout does not work that way. The base signature fee is the part that is owed for the signatures themselves. Anything the sender added so a leader might include the transaction sooner sits elsewhere. SOL that an account holds in order to remain rent-exempt is not a fee at all.
On the window desk we use a sample from drawer A when someone has no printout of their own. Drawer A holds single-signature transfers. We ask the visitor to point at the fee total and then to cover it with a card. They write 5,000 in the signature column and only then look back at the total. If the total is larger, the difference has a home in another column. If it matches, the receipt was a base fee and nothing more.
What we leave off the first pass
We do not open with compute units. We do not talk about which validator led the slot. Those facts matter on some receipts, and they wait until the signature count is written down. People who try to explain the whole page in one breath usually fold the base fee into the priority fee and then cannot say which lamports did which job.
The signature line is also the part of the fee that does not depend on how busy the network felt that hour. Congestion shows up when someone attaches a priority fee. The 5,000 lamports per signature are the steady line. That steadiness is why we teach it first, and why a Saturday table begins with the same arithmetic before the second sample comes out of the folder.