Crypto amounts live in many denominations, and mixing them up costs real money. This converter moves a value across all Bitcoin units (satoshi, mBTC, BTC) or all Ethereum units (wei, gwei, ether) at once, with an optional USD value from a price you supply.
How it works
Each chain has a smallest base unit, and every denomination is a fixed power of ten away from it:
Bitcoin base = satoshi
1 BTC = 100,000,000 satoshi (10^8)
1 mBTC = 100,000 satoshi (10^5)
Ethereum base = wei
1 ether = 1,000,000,000,000,000,000 wei (10^18)
1 gwei = 1,000,000,000 wei (10^9)The wei base is handled with big integers because an ether expressed in wei has 19 digits — beyond exact floating-point range — so conversions stay precise.
Where each unit appears in practice
Understanding not just what the units mean but where you actually encounter them prevents real mistakes:
Bitcoin
| Unit | Common context |
|---|---|
| satoshi | Lightning Network amounts, micropayments, wallet granularity |
| mBTC | Casino-style displays, some exchanges for mid-range amounts |
| BTC | Exchange order books, wallet balances, price quotes |
Ethereum
| Unit | Common context |
|---|---|
| wei | EVM storage, Solidity calculations, raw JSON-RPC values |
| gwei | Gas prices (e.g. “20 gwei base fee”) — the unit wallets display |
| ether | User-facing balances, transaction value, DEX token prices |
Knowing which unit an API or smart contract returns is critical. The Ethereum eth_getBalance RPC returns wei; MetaMask displays ether; gas prices in wallets show gwei. A misread unit is not a rounding error — it is a factor of 10⁹ or 10¹⁸.
Worked examples
Pricing a transaction fee. A gas limit of 21,000 at a 20 gwei base fee costs:
21,000 × 20 gwei = 420,000 gwei = 0.00042 etherAt an ether price of $3,200, the fee is approximately $1.34. Type 420,000 into the gwei field to confirm.
Checking a Solidity value. A contract stores a token price as 2000000000000000 wei. Type that into the wei field and the tool shows 0.002 ether — the readable price.
Bitcoin micropayment. A Lightning invoice for 500 satoshi: type 500 in the satoshi field to see it equals 0.000005 BTC or 5 mBTC, and at a hypothetical BTC price of $60,000, about $0.03.
Why big integers matter for wei
JavaScript’s Number type can represent integers exactly up to 2^53 − 1 (about 9 quadrillion). One ether in wei is 1,000,000,000,000,000,000 — 10^18 — which exceeds that limit by roughly 100x. Naive float arithmetic silently rounds to the wrong value. This tool uses BigInt for wei operations to avoid that rounding, ensuring conversions like 3141592653589793238 wei convert correctly rather than to an approximate value.
Tips
- Enter the price yourself. No API call is made for the exchange rate; paste the current BTC or ETH price from any source. This keeps the tool usable offline and avoids stale-rate errors.
- Cross-check contract inputs. When writing a Solidity function that takes a wei amount, type the human-readable ether amount into this converter first, then copy the wei output into your test.
- All conversions run in your browser — nothing is stored or sent.