Mempool Fee Estimator
How This Works
Based on Bitcoin network data from the last 3 years, this calculator estimates the optimal fee rate (satoshis per virtual byte) based on current mempool congestion and your target confirmation time.
When you send a Bitcoin transaction and it takes hours-or even days-to confirm, it’s not because the network is broken. It’s because the mempool is full.
What Is the Mempool?
The mempool, short for memory pool, is where unconfirmed transactions wait to be picked up by miners and added to the next block. Think of it like a waiting room at a busy airport: everyone has a ticket (a transaction), but only a limited number of planes (blocks) can take off every 10 minutes. If too many people show up at once, the line gets long. That’s mempool congestion. Every full node on the Bitcoin network keeps its own mempool. There’s no single global mempool. That means if you check your transaction on mempool.space and it shows 80,000 transactions waiting, another node might show 75,000. Why? Because each node has its own rules for what it accepts and how long it holds onto transactions. Bitcoin Core, the most widely used software, sets a default mempool size limit of 300 MB. But that’s not 300 MB of raw transaction data. It includes metadata, indexes, and pointers-so the actual number of transactions stored is less than you’d think. A 300 MB mempool can hold around 150,000 to 200,000 transactions, depending on their size. Once it hits that limit, the node starts kicking out the cheapest transactions first to make room.How Mempool Congestion Works
Congestion happens when more transactions are sent than can fit in the next few blocks. Each block on Bitcoin is limited to about 4 MB (or 1 MB of legacy data, but up to 4 MB with SegWit). At 10-minute intervals, that’s roughly 1,800 to 2,500 transactions per block, depending on complexity. When demand spikes-like during a major NFT drop, a crypto price surge, or a big exchange withdrawal event-transactions flood in faster than blocks can be mined. The mempool grows. And as it grows, fees climb. Miners don’t care about fairness. They care about profit. So they pick transactions with the highest fee rates-measured in satoshis per virtual byte (sat/vB). If you send a transaction with 5 sat/vB, and the mempool is full, yours might sit there for hours. Someone else paying 150 sat/vB? Their transaction gets confirmed in minutes. Blockchain.com’s data shows that when the mempool exceeds 100,000 transactions, confirmation times jump to over 30 minutes. At 150,000+, it’s common to wait 4-12 hours. And if you’re paying only the minimum relay fee of 1 sat/vB? You could be waiting 72+ hours, as seen during the April 2023 congestion spike.
Why Mempool Size Matters
Mempool size isn’t just a number-it’s a leading indicator. It tells you what’s coming before fees spike. If you see the mempool growing steadily over 15-30 minutes, you know fees are about to rise. Waiting until your transaction is stuck is too late. Here’s what different mempool sizes mean in practice:- Under 20,000 transactions: Low congestion. Fees around 5-10 sat/vB. Confirmed in 1-2 blocks.
- 20,000-50,000 transactions: Moderate congestion. Fees 15-30 sat/vB. Confirmed within 1-2 hours.
- 50,000-100,000 transactions: High congestion. Fees 40-80 sat/vB. Wait 2-6 hours.
- Over 100,000 transactions: Severe congestion. Fees 100-200+ sat/vB. Wait 6-24+ hours.
How to Handle Congestion
You don’t have to pay whatever the market demands. Here’s how to navigate it:- Check mempool.space before sending. Look at the current mempool count and the fee estimator. It shows you what fee gets you confirmation in 1, 5, or 60 minutes.
- Use SegWit or Taproot addresses. These reduce transaction size by 20-40%, meaning you pay less in fees for the same transaction. A typical SegWit transaction is 140 vbytes; a legacy one is 225 vbytes. That’s 38% less fee.
- Batch your transactions. If you’re sending Bitcoin to multiple people, combine them into one transaction. Blockstream’s data shows batching cuts total transaction count by 30-50%, saving you money and reducing network load.
- Use Replace-by-Fee (RBF). If your transaction is stuck, you can bump the fee. Most wallets support this. You’re not canceling-it’s just upgrading your priority.
- Child-Pays-for-Parent (CPFP). If you sent a low-fee transaction to someone, and they send a new transaction spending that output with a high fee, miners will prioritize the whole chain. Useful for merchants or wallets stuck in congestion.
maxmempool from 300 MB to 500 MB to hold more transactions. But that uses more RAM. Lowering minrelaytxfee below 1 sat/vB lets you accept cheaper transactions-but you might get flooded with spam.
How Other Blockchains Handle It
Bitcoin’s mempool is fee-driven. Ethereum is different. Since EIP-1559, it uses a base fee that burns with each block and a tip for miners. The base fee adjusts dynamically based on block usage. If blocks are over 50% full, the base fee goes up. If under, it drops. That makes fees more predictable, but doesn’t eliminate congestion. Solana takes another route. It doesn’t use a mempool like Bitcoin. Transactions are processed in parallel by validators, and the network prioritizes speed over decentralization. That’s why Solana can handle thousands of transactions per second-but it’s also why it crashes when overloaded. Layer-2 solutions like the Lightning Network are the real answer to Bitcoin’s mempool problem. During the 2022-2023 congestion spikes, Lightning Network capacity grew 230%. Now, over 40% of Bitcoin’s value transfers happen off-chain, according to Arcane Research. That’s not a workaround-it’s the future.What’s Next for Mempools?
Bitcoin Core 24.0 (released in early 2023) improved how mempools handle eviction during congestion. Version 25.0, coming in late 2024, will add smarter resource management to prevent nodes from crashing under pressure. Taproot adoption is rising. Since November 2021, over 70% of new Bitcoin transactions use Taproot. These transactions are smaller and more efficient, reducing average size by 15-25%. That means more transactions fit in each block-slowing mempool growth without needing a hard fork. Tools like mempool.space are adding predictive models. By analyzing historical congestion patterns, they’ll soon be able to forecast fee spikes hours in advance. That’s huge for exchanges, wallets, and users who need reliable timing. The bottom line? Mempool congestion isn’t a bug-it’s a feature. It’s how Bitcoin ensures security and fair resource allocation. High fees aren’t a failure. They’re the market telling you: “This network is in demand.” But that doesn’t mean you have to pay more than you need to. With the right tools and timing, you can send your Bitcoin quickly, cheaply, and without stress.What is a normal mempool size for Bitcoin?
A normal mempool size ranges from 15,000 to 40,000 transactions during low-traffic periods. During average usage, it sits between 40,000 and 60,000. Anything above 100,000 signals high congestion and likely delays.
Why do some transactions take days to confirm?
Transactions with fees below the network’s minimum relay rate (1 sat/vB) get pushed to the back of the queue. During congestion, nodes evict low-fee transactions first. If your fee is too low and you don’t bump it, your transaction can sit for days-sometimes over a week-before being dropped.
Can I speed up a stuck transaction without paying more?
Not directly. But if you control the receiving wallet (like in a CPFP scenario), you can create a new transaction spending the stuck output with a higher fee. Miners will then prioritize the whole chain. This works best if the original transaction used RBF or if the recipient cooperates.
Does mempool congestion affect altcoins too?
Yes, but less severely. Most altcoins have smaller networks and faster block times, so congestion clears quicker. Ethereum uses EIP-1559 to smooth fees. Litecoin and Dogecoin have larger blocks than Bitcoin, so they handle spikes better. But any blockchain with a mempool and block limits can experience congestion.
Is a large mempool a sign Bitcoin is failing?
No. A large mempool means Bitcoin is in high demand. It’s proof the network is being used. The fee market ensures security-miners are paid to verify transactions, and higher fees make attacks more expensive. Congestion isn’t a flaw; it’s a signal of success. The real issue is when users don’t know how to respond to it.
How often does Bitcoin’s mempool get this full?
It happens several times a year, usually during major events: Bitcoin ETF approvals, large exchange withdrawals, NFT launches, or sudden price surges. The biggest spikes were in 2017, 2021, and early 2023. Since 2022, congestion has become more predictable due to better tools and increased use of layer-2 solutions.
