Satoshi ↔ USD.
You don't need a whole Bitcoin.

This tool runs entirely in your browser: nothing you enter is sent to any server. The price comes from the site’s own data file (/data/btc-tip.json, the latest saved daily close); no price service is contacted.

A fetched price is reused for 60 seconds across pages and is not refreshed while the page stays open. Until a price arrives, and whenever all four sources fail or 5 seconds pass without one, the tool uses $81,262; after either failure the page skips the request for the next 5 minutes. $81,262 is the Coin Metrics end-of-day USD price for 2026-09-19 in the site's data snapshot^[1]. One bitcoin is 100,000,000 sats in Bitcoin Core's consensus code^[2]. Conversions:

• From sats: sats rounded to a whole sat; BTC = sats ÷ 100,000,000; USD = BTC × price.
• From BTC: sats = BTC × 100,000,000, rounded to a whole sat; BTC and USD are then worked from that whole-sat amount.
• From USD: sats = USD ÷ price × 100,000,000, rounded to a whole sat; BTC = sats ÷ 100,000,000.

Rounding is to the nearest whole sat, with halves rounding up. Calculated fields show BTC to 8 decimals and USD to the nearest cent. A typed amount is read digit by digit and the dollar side is worked in exact decimal arithmetic, so every amount up to the 21,000,000 BTC cap converts exactly, to the sat and to the cent. The field you type in keeps what you typed; when a sats or BTC entry had to be rounded to a whole sat, a note under the fields gives the amount converted; a USD entry worth less than half a sat gets a note that it rounds to 0 sats. An amount above 21,000,000 BTC is converted anyway, with a note that it is more than will ever exist. A negative amount is rejected with a note and the other two fields are cleared; an empty field clears the other two. The "What can sats buy" rows apply the same USD formula to fixed amounts from 1,000 sats to 1 BTC, shown to 4 decimals under $1, to the cent from $1, and in whole dollars from $1,000; their labels are illustrations, not price data. When the saved price loads, the tool re-converts from the field last typed in (sats if none), so a typed BTC or USD amount is kept and the other two fields update.

Verify the methodology or inspect the source code in your browser's dev tools.