Bitcoin: 100 Million Satoshis and No Decimals At All
The first thing to understand is that Bitcoin's software has no concept of "1 BTC". The protocol counts everything in its smallest indivisible unit — the satoshi — and "1 BTC" is simply the human display convention for 100,000,000 satoshis.
| Unit | In satoshis | In BTC |
|---|---|---|
| 1 satoshi (sat) | 1 | 0.00000001 |
| 1 bit (μBTC) | 100 | 0.000001 |
| 1 mBTC (millibitcoin) | 100,000 | 0.001 |
| 1 BTC | 100,000,000 | 1 |
Why integers? Because floating-point arithmetic is catastrophic for money. In floating point, 0.1 + 0.2 famously equals 0.30000000000000004 — rounding errors like that, compounded across a monetary network, would be fatal. Every serious financial system counts integer minor units (cents, paise, satoshis); Bitcoin just made the minor unit very small.
The choice of 10⁸ gives Bitcoin's 21 million coin cap a total supply of 2.1 quadrillion satoshis — enough granularity that even with one BTC worth six figures, a satoshi remains a fraction of a cent, keeping micro-amounts expressible. The Lightning Network goes further, accounting internally in millisatoshis (1/1000 sat) for routing math, though on-chain settlement rounds back to whole sats.
Culturally, "sats" have become the practical denomination — "stacking sats", coffee priced at 4,200 sats — partly because whole numbers feel more natural than 0.00004200 BTC. Which, as we will see in the unit-bias section, is precisely the psychology at work.
Ethereum: 18 Decimals and a Unit for Every Job
Ethereum went further: 1 ETH = 10¹⁸ wei — a quintillion. Like Bitcoin, the protocol counts only integers (wei); unlike Bitcoin, it reserved enough decimal places that no conceivable value is too small to represent. The three units that matter in practice:
| Unit | In wei | Used for |
|---|---|---|
| wei | 1 | Protocol-level accounting, smart contract math |
| gwei (gigawei) | 10⁹ | Gas prices — the fee market's natural denomination |
| ETH (ether) | 10¹⁸ | Human-facing balances and prices |
(The full ladder includes kwei, mwei, szabo, and finney — named after cryptography pioneers — but you can spend years in Ethereum without meeting them.)
The 18-decimal convention spread beyond ETH itself: the ERC-20 token standard defaults to 18 decimals, so a wallet showing "2.5 tokens" is rendering the integer 2500000000000000000 with the decimal point inserted 18 places from the right. Two practical consequences for anyone touching crypto programmatically:
- Never parse token amounts as floats. JavaScript's Number loses integer precision above 2⁵³ — and 1 ETH in wei (10¹⁸) is already past it. Use BigInt or decimal libraries; every major crypto library (ethers.js, viem, web3.py) does.
- Not every token uses 18. USDC and USDT use 6 decimals; WBTC uses 8. Assuming 18 for a 6-decimal token misprices amounts by a factor of a trillion — a real bug class that has drained real contracts.
Gas: Why Fees Are Priced in Gwei and How to Read Them
Every Ethereum operation costs gas — a unit of computational work. A simple ETH transfer costs exactly 21,000 gas; swapping on a DEX might cost 150,000–300,000; deploying a contract, millions. Your fee is:
fee = gas used × gas price
gas price (post-EIP-1559) = base fee (burned, set by protocol)
+ priority tip (to the block proposer)
Example: 21,000 gas × 12 gwei = 252,000 gwei
= 0.000252 ETH (≈ $0.60–0.90 at recent ETH prices)Gwei exists because it is the Goldilocks denomination: quoting that fee as 252,000,000,000,000 wei is unreadable, and as 0.000252 ETH invites decimal-place mistakes. "12 gwei" is a number humans can compare at a glance.
What actually moves gas prices is demand for block space: the EIP-1559 base fee rises when blocks run full and falls when they empty, so fees spike during NFT mints, airdrops, and market crashes (everyone rushing to trade or unwind at once), and fall to low single-digit gwei on quiet weekends. Practical fee hygiene:
- Non-urgent transactions are cheapest at off-peak hours (weekends, outside US/EU business hours) — timing alone often cuts fees several-fold.
- Layer 2 networks (Arbitrum, Optimism, Base) execute the same operations for cents — they batch thousands of transactions into one L1 proof, which is why most retail activity migrated there.
- Beware the units when setting manual fees. Confusing gwei with wei, or setting a priority tip in ETH instead of gwei, has produced legendary accidental fees — wallets warn, but only if you read the warning.
- Bitcoin's fee logic differs: fees are priced in sats per virtual byte of transaction size, not per computational step — a transaction with many inputs costs more regardless of its monetary value.
Unit Bias: The Psychology Trap Priced Into Cheap Coins
Unit bias is the documented tendency to prefer owning whole units of something rather than fractions — and in crypto it is a costly, actively exploited bug in human reasoning.
The pattern: a newcomer with $500 sees Bitcoin at $100,000 ("I can only afford 0.005 — too expensive!") and a token at $0.0001 ("I can buy five million of them!"). The whole-number holding feels more substantial and the cheap token feels like early Bitcoin. Both feelings are innumerate:
- Price per unit is meaningless without supply. Value per coin = market cap ÷ circulating supply. A $0.0001 token with 10 trillion tokens is a $1 billion project; doubling your money requires it to become a $2 billion project — exactly as hard as any $1B asset doubling. The low unit price signals nothing except a large supply.
- "It only needs to reach $1" is the unit-bias battle cry — for a 10-trillion-supply token, $1 implies a $10 trillion market cap, several times all of Bitcoin. Checking implied market cap kills most such fantasies in one division.
- Meme-token economics weaponize this deliberately: supplies of quadrillions exist precisely so the unit price is microscopic and buyers feel rich holding billions of units.
- The defense is denominating consistently: think in dollars invested and market cap, or think in sats — $500 is 500,000 sats regardless of Bitcoin's unit price, and 0.005 BTC is not "less Bitcoin" than 5M UselessCoin is "more".
Satoshi-denomination enthusiasts point out, correctly, that Bitcoin itself suffers reverse unit bias: at a six-figure BTC price, newcomers feel "priced out" of an asset they could buy $10 of — one reason the community increasingly quotes prices in sats. None of this section tells you what to buy; it tells you how to see through the single most common pricing illusion in the asset class.