Blockchain
Block
A collection of cryptocurrency transactions bundled together and added to the blockchain. Each block contains transaction data, a timestamp, and a cryptographic link to the previous block.
Last updated: January 5, 2025
What is a Block?
A block is a bundle of cryptocurrency transactions that have been verified and recorded on the blockchain. Think of it as a page in a ledger—once written, it becomes a permanent part of the record and links to all previous pages.
Block Structure
Components
Block Header:
├── Previous block hash (link to chain)
├── Merkle root (summary of transactions)
├── Timestamp
├── Difficulty target
└── Nonce (Proof of Work only)
Block Body:
├── Transaction count
└── Transaction listKey Elements
| Component | Purpose |
|---|---|
| Previous hash | Links to prior block |
| Timestamp | When block was created |
| Transactions | Actual transfer data |
| Merkle root | Transaction summary |
| Nonce | Mining solution (PoW) |
Block Creation Process
Proof of Work (Bitcoin)
- Transactions collected into mempool
- Miners select transactions
- Miners compete to solve puzzle
- Winner broadcasts block
- Network validates and accepts
Proof of Stake (Ethereum)
- Transactions collected
- Validator randomly selected
- Validator proposes block
- Other validators attest
- Block finalized
Block Parameters by Network
| Network | Block Time | Block Size | Transactions/Block |
|---|---|---|---|
| Bitcoin | ~10 min | 1-4 MB | 2,000-4,000 |
| Ethereum | ~12 sec | Variable (gas) | 100-500 |
| Solana | ~400 ms | Variable | 1,000+ |
| BNB Chain | ~3 sec | Variable | 500+ |
Why Block Size Matters
Larger Blocks
- More transactions per block
- Lower fees during congestion
- Requires more bandwidth/storage
- Slower propagation
Smaller Blocks
- Fewer transactions per block
- Higher fees during congestion
- More decentralized (easier to run node)
- Faster propagation
Block Rewards
Validators/miners receive:
- Block subsidy: New coins created
- Transaction fees: Fees from included transactions
Bitcoin Block Rewards
| Era | Block Reward |
|---|---|
| 2009-2012 | 50 BTC |
| 2012-2016 | 25 BTC |
| 2016-2020 | 12.5 BTC |
| 2020-2024 | 6.25 BTC |
| 2024+ | 3.125 BTC |
Block Explorers
View blocks on:
- Bitcoin: blockchain.com, mempool.space
- Ethereum: etherscan.io
- Multi-chain: blockchair.com
Block Confirmations
More blocks after your transaction = more secure:
| Confirmations | Bitcoin | Ethereum |
|---|---|---|
| 1 | ~10 min | ~12 sec |
| 3 | ~30 min | ~36 sec |
| 6 | ~60 min | ~72 sec |
Exchanges like Coinbase and Binance require varying confirmations before crediting deposits.
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