FuelLabs/fuel-core · error

The final fee is too big to fit into `u64`

Error message

The final fee is too big to fit into `u64`

What it means

After computing the final gas for the tx, the assembler converts gas to fee (gas_to_fee, computed in U256 using gas_price and the chain's gas_price_factor) and converts the result back to u64. The error fires when the computed fee exceeds u64::MAX — an arithmetic impossibility for sane gas prices.

Source

Thrown at crates/fuel-core/src/schema/tx/assemble_tx.rs:945

                        total_base_asset.checked_add(amount).ok_or_else(|| {
                            anyhow::anyhow!(
                        "The total base asset amount used by the transaction is too big"
                    )
                        })?;
                }
            }
        }

        loop {
            let max_gas = self.tx.max_gas(&gas_costs, &fee_params);
            let max_gas_with_reserve = max_gas.saturating_add(self.arguments.reserve_gas);

            let final_gas = max_gas_with_reserve.min(max_gas_per_tx);
            let final_fee =
                gas_to_fee(final_gas, self.arguments.gas_price, gas_price_factor);
            let final_fee = u64::try_from(final_fee)
                .map_err(|_| {
                    anyhow::anyhow!("The final fee is too big to fit into `u64`")
                })?
                .saturating_add(self.tx.tip());

            let need_to_cover = final_fee.saturating_add(self.base_asset_reserved);

            if need_to_cover <= total_base_asset {
                break
            }

            let remaining_input_slots = self.remaining_input_slots()?;
            if remaining_input_slots == 0 {
                return Err(CoinsQueryError::MaxCoinsReached {
                    owner: fee_payer_account.owner(),
                    asset_id: base_asset_id,
                    collected_amount: total_base_asset.into(),
                    max: self.arguments.consensus_parameters.tx_params().max_inputs(),
                }
                .into());

View on GitHub (pinned to b9d4d170da)

Solutions

1. Re-check the gas price you send: use the value from the node's estimateGasPrice, not a hand-scaled constant
2. Lower the tx's gas ceiling (script gas limit, witness/data usage) so gas x price fits u64
3. If you operate the chain, verify consensus parameter gas_price_factor is set correctly

Example fix

// before
await client.assembleTx(txBytes, { requiredBalances, gasPrice: 1_000_000_000_000n }); // wrong scale

// after
const { gasPrice } = await client.queryEstimateGasPrice(blockHorizon);
await client.assembleTx(txBytes, { requiredBalances /* node-derived gas price */ });

// client-side mirror of gas_to_fee: fee = gas * gasPrice / gasPriceFactor
const fee = (BigInt(finalGas) * gasPrice) / BigInt(gasPriceFactor);
if (fee > 2n ** 64n - 1n) throw new Error(`fee ${fee} overflows u64; lower gas price or gas limit`);

catch (e) { if (/final fee is too big to fit into/.test(e.message)) { /* use node-reported gas price, reduce script gas limit / tip */ } else throw e; }

When it happens

Trigger: final_gas * gas_price / gas_price_factor > u64::MAX: an extreme gas_price combined with a large gas estimate, or a misconfigured gas_price_factor (e.g. 0-adjacent values in a custom chain making the division inflate the result).

Common situations: Passing a wrongly-scaled gas price (unit confusion, e.g. sending the full-token amount instead of per-gas amount); custom chains with a broken gas_price_factor consensus parameter.

Related errors

• Unable to add more inputs because reached the maximum allowe
• The total base asset amount used by the transaction is too b
• The total base asset amount became too big when tried to cov
• The transaction has more outputs than allowed by the consens
• The fee address index is out of bounds

AI-assisted analysis of FuelLabs/fuel-core@b9d4d170da (2026-08-16). Data as JSON: /api/errors/d2713b956aeb707d. Report an issue: GitHub.