Unit of Account is money’s function as a common unit for expressing prices and debts. It does not mean an organisation or person keeping accounts. What matters is the unit in which an amount is set, not merely what you pay with or which currency the screen displays.
BTC is bitcoin’s currency symbol. The Bank of England, the UK’s central bank, distinguishes the measure of prices from the means of exchange and storing value. Medium of Exchange describes what people use to transfer payment; Store of Value asks whether resources kept today retain value into the future. These functions are connected but need not belong to the same asset. Our café can fix its price in crowns while accepting BTC. Holding or paying bitcoin therefore does not establish that a merchant actually sets prices, wages or debts in bitcoin. [1]
If every business listed only what it would exchange its product for, comparison would be cumbersome. The European Central Bank (ECB) explains that a common unit enables goods to be priced and prices compared. Our four goods have 4 × 3/2 = 6 pairs of exchange ratios. Four price tags in a shared unit outside those goods, such as crowns, allow those ratios to be derived. If A = 20 and B = 50, then B/A = 2.5: the second good costs that multiple of the first. This does not mean people value them equally. Price comparisons do not replace personal needs and preferences. [2]
CZK is the international currency code for the Czech crown. Take our own bill of 1000 CZK at an agreed rate of 1 000 000 CZK per BTC. Payment is 0.001 BTC. If the rate changes to 1 250 000 before a new conversion, payment becomes 0.0008 BTC, provided the agreement still fixes 1000 CZK and uses the new rate. These are deliberately simple figures without fees, not current quotes. The timing of the rate and the offer’s validity matter. An amount on an earlier payment request may cease to apply after expiry. A fixed crown price does not itself fix the bitcoin amount. [1]
Instead, suppose the agreement fixes 0.001 BTC. An exchange-rate change leaves that bitcoin obligation unchanged. In the previous model, however, its crown equivalent increases from 1000 to 1250 CZK. A converted display does not rewrite the contract: the indicative value in another currency changes, not the agreed amount. Separate what you owe, how the app displays it and what you are allowed to use for settlement. For a particular purchase, the agreed terms matter, not simply the presence of a bitcoin button. [1]
The Bitcoin Core software counts 1 BTC as 100 000 000 satoshi. Thus 0.001 BTC is 100 000 satoshi. Satoshi, often shortened to sat, is a smaller unit of the same bitcoin; changing the display does not add coins. A BIP (Bitcoin Improvement Proposal) is a documented proposal concerning Bitcoin. BIP 176 describes a bit as 100 satoshi, making the same amount 1000 bits. At this review the document’s status is Complete, meaning a completed document, but adoption is optional: it is neither a new currency nor a mandatory protocol change. Do not confuse this monetary bit with the computing unit for data. Always check both number and unit before sending. [3] [4]
A more technical example shows why a wallet’s display setting is not enough. BIP 321 describes bitcoin URIs, machine-readable payment links also used in QR codes. Their amount parameter uses decimal BTC with a period and no commas. The notation amount=0.001 means 0.001 BTC, or 100 000 satoshi, even when the screen uses satoshi. Writing amount=100000 would request a completely different BTC amount. BIP 21 is replaced by BIP 321. Nor does the link alone reveal whether the original price agreement was in crowns or bitcoin; it conveys payment instructions. [5]
Our illustrative basket rises from 100 to 125 units, an increase of 25%. A balance of 100 now buys 0.8 baskets rather than a whole one: purchasing power has fallen by 20%. Neither the unit’s name nor the account balance changed. Purchasing Power describes what your money actually buys, while the accounting function lets prices be written down and compared. Storing value concerns the future: whether money set aside will still buy goods later. Keep display changes, exchange-rate changes and rising goods prices separate. Any one can occur without the others. [2]
Ask whether the merchant calculates underlying prices and obligations in bitcoin or simply converts conventional currency at checkout. A stablecoin linked to a conventional currency is a digital token designed to maintain a target exchange rate against that currency. The Bank for International Settlements (BIS) explains in its 2022 report that stablecoins linked to traditional currencies borrow their pricing unit. A digital payment instrument therefore need not introduce a new unit of account; targeting an exchange rate does not guarantee maintaining it either. For BTC, look at actual agreed prices and debts. Transaction counts or a website’s currency switch are insufficient. The agreement’s substance reveals who bears the exchange-rate risk. [6]
For the clearest picture, read this entry together with Medium of Exchange, Store of Value, Satoshi, Purchasing Power. The reverse links also lead from Satoshi, Sound money, Medium of Exchange, Store of Value.