Why exact arithmetic matters
JavaScript numbers are 64-bit floats and lose precision above 2^53 (about 9 × 10^15). One ether is 10^18 wei, so float maths silently corrupts ordinary balances. Every conversion here uses BigInt and decimal strings. If an input has more fractional digits than the unit allows, the converter refuses and says by how much, rather than rounding.
Token decimals are untrusted metadata
An ERC-20 token's decimals() value is optional and set by the token contract. USDC uses 6, many tokens use 18, some use 0 or 8. The token tool will not convert until you supply decimals, records where the value came from, and keeps showing raw base units alongside.
QUANTITY versus DATA
Ethereum JSON-RPC uses two hex encodings. QUANTITY is a compact number: "0x0" is zero, leading zeros are invalid. DATA is bytes with two hex digits per byte: "0x" is empty, odd lengths are invalid. "0x0" and "0x" are different values; the hex tool shows how a string reads under each rule.
Fees on hypothetical inputs
The fee calculator applies the EIP-1559 rule effective price = min(maxFeePerGas, baseFee + maxPriorityFeePerGas), splits the burned base fee from the tip, and adds EIP-4844 blob gas at 131,072 per blob. You type the base fee; nothing is fetched.
Questions
How many wei are in one gwei and one ether?
1 gwei = 1,000,000,000 wei (10^9). 1 ether = 1,000,000,000,000,000,000 wei (10^18).
Why does 0.0000000001 gwei fail?
Gwei has 9 decimal places relative to wei, and wei is indivisible. That value would need a fraction of a wei, so the converter refuses rather than rounding to zero.
Can I convert a token amount without knowing its decimals?
You can see the raw base-unit integer, but the human-readable amount needs decimals. Assuming 18 would be wrong for USDC (6) and WBTC (8), so the tool asks.
Is the gas calculator showing current fees?
No. Every input is a value you type. Use it to reason about a fee you already have from a provider or receipt.