Using KuCoin Web3 Wallet

Gas Estimation: How It Works and How to Set It?

Last updated: 12/03/2025

1. Core Concepts 

1.1 EVM gas (Ethereum & EVM chains)

  • Every transaction consumes gas units.
  • With EIP-1559, your fee ≈ gas used × (base fee + priority fee). 
  • Gas limit is the cap you allow to be consumed (estimate is conservative). Gas used is what actually gets burned.
  • Wallets estimate:
    • Gas limit via simulation (e.g., eth_estimateGas).
    • Prices via recent fee history/tip estimators (sets maxFeePerGas and maxPriorityFeePerGas).
  • Rule: set a sane max fee ceiling, and a priority fee (tip) appropriate for current demand.

1.2 L2 rollups (OP Stack/Base, Arbitrum, etc.)

  • Your total cost = L2 execution gas + L1 data fee (publishing your tx data to Ethereum).
  • Since EIP-4844, rollups pay a separate blob gas market for L1 data; this component can spike independently of L2 execution.

1.3 Solana (compute units + priority)

  • Fees = base fee per signature + optional priority fee. 
  • Priority fee = compute units (CU) × price per CU.
  • A right-sized CU limit and realistic CU price improves inclusion without overpaying.

2. When Should I Adjust the Estimate?

Scenario

Starting point (guideline)

EVM – normal swaps

Use wallet default(average) estimate (auto base/priority).

EVM – urgent

Nudge priority fee up in small steps; keep max fee comfortably above (base+priority).

EVM – congested / pending

Retry with a slightly higher priority fee or wait off-peak; avoid 10× jumps.

L2 (OP/Base)

Defaults usually work; if stuck, add a small priority fee. L1 data fee may be the bottleneck.

L2 (Arbitrum)

Spikes often come from L1 data; try off-peak or a leaner route.

3. Why “Underpriced” or “Urgent” Can Still Fail

Your tx competes in a mempool with variable rules and demand; paying more improves odds but never guarantees the next block.

  • State changed after simulation → contract path now reverts regardless of fee.
  • L2 L1-data spikes → inclusion delayed even when L2 execution is cheap.
  • Solana prioritization → too-low CU price or oversized CU limit (wasting budget) can hurt inclusion.

4. KuCoin Web3 Wallet: Recommended Settings (General)

Path: KuCoin App → top bar “Web3” → bottom bar → Swap

Settings: Swap screen → Network Fee

1. Start with the wallet’s Auto gas estimate. 

2. Need speed? On EVM, choose Fast.

3. Keep a reasonable max fee buffer (EVM); don’t massively overbid. 

4. Do a small test swap before scaling size. 

Tip: Persistent pending/reverts usually point to slippage/price impact. Try a deeper route or split the order.

5. Troubleshooting (6 Practical Moves)

  1. EVM underpriced/pending: Slightly increase priority fee or max fee, or cancel & replace.
  2. L2 spikes: Wait for blob/data fees to normalize; retry.
  3. Solana slow: Raise CU price; right-size CU limit.
  4. Frequent reverts: Check slippage, token taxes, price impact (not a gas issue).
  5. RPC hiccups: Switch RPC or try later.
  6. Housekeeping: Keep app updated; avoid stale networks/custom RPCs that mis-estimate.

6. FAQs

6.1 Does paying more guarantee the next block? 

No. It raises your priority but doesn’t guarantee inclusion under heavy demand. 

6.2 Why is actual fee lower than my max? 

With EIP-1559, you set a ceiling; you only pay what’s needed given the current base fee + tip. 

6.3 Why do L2 fees jump randomly? 

The L1 data component (blobs) has its own fee market and can spike independently. 

6.4 Solana: should I max CU price/limit? 

No. Use just enough to be included; oversizing wastes fees without proportional speed gains.

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