<p>Sure.</p>

<p><a href="https://blockchain.info/block/00000000000000000fc5e782386b679ad5833ea2cddf4e06ebb403d725655a69" rel="nofollow">This</a> is one such block. It's 312 kB.</p>

CC BY-SA 3.0
2015-11-01T03:38:58.590Z
2015-11-01T03:38:58.590Z
Nick ODell
<p>Blocks have to have at least one transaction: They must contain a coinbase which is the transaction that spends the block reward.</p>

<p>For example this <a href="https://blockchain.info/block-index/512049/00000000000000000429a0c4fbe735b2d8b493daedf0207728543f748c262437" rel="nofollow">block with only one transaction</a>  is only    <code>0.246 kB</code>.</p>

CC BY-SA 3.0
2015-11-02T19:56:10.450Z
2015-11-02T19:56:10.450Z
Murch
<p>Yes.  Let's calculate the minimum size of a block:</p>

<ul>
<li><p>The <a href="https://bitcoin.org/en/developer-reference#block-headers">block header</a> must be exactly 80 bytes.  This is the only part of the block that miners actually mine; the rest of the block is data that the header securely references.</p></li>
<li><p>The transaction count.  This isn't part of the block header and it isn't part of the block data, but it's part of the peer-to-peer protocol <a href="https://bitcoin.org/en/developer-reference#block">block message</a> so it gets counted towards the block size.  For blocks with 253 or fewer transactions, this is 1 byte.</p></li>
<li><p>The coinbase transaction, the only required transaction in a block.  The coinbase transaction has the following fields with these minimum values:</p>

<ul>
<li>4 bytes -- version field</li>
<li>1 byte  -- number of inputs (always 1 for coinbase transactions)</li>
<li>32 bytes -- <a href="https://bitcoin.org/en/developer-reference#outpoint">outpoint</a> txid; always 32 0x00 bytes for coinbase transactions</li>
<li>4 bytes -- outpoint index; always 4 0xff bytes for coinbase transactions</li>
<li>1 byte -- number of bytes in coinbase field (input script); always 1 byte for coinbase transactions because there's a 100-byte limit</li>
<li>4 bytes -- block height as a data push; required by <a href="https://github.com/bitcoin/bips/blob/master/bip-0034.mediawiki">BIP34</a></li>
<li>4 bytes -- <a href="https://bitcoin.org/en/developer-guide#locktime-and-sequence-number">sequence number</a></li>
<li>1 byte -- number of outputs, we're not going to have any (making the block reward and transaction fees paid in this block permanently unspendable; no real miner would do this)</li>
<li>4 bytes -- <a href="https://bitcoin.org/en/developer-guide#locktime-and-sequence-number">locktime</a></li>
<li><strong>Total:</strong> 55 bytes</li>
</ul></li>
</ul>

<p><strong>Total minimum block size:</strong> 80 + 1 + 55 = 136 bytes</p>

<p>Practically, the smallest reasonable blocks are in the 180-byte range.</p>

CC BY-SA 3.0
2015-11-01T07:07:32.427Z
Empty `vout` would make the transaction [invalid](https://github.com/bitcoin/bitcoin/blob/master/src/main.cpp#L725-L726). You would need to have one output of 0 BTC, 0 length, null script for a total 9 bytes (8 byte value, one byte VarInt). This would also be an anyone can spend output as a null script can be satisfied by pushing anything to the stack.
Claris
CC BY-SA 3.0
2015-11-01T04:12:11.827Z
2015-11-01T04:12:11.827Z
David A. Harding
<p>Can a Bitcoin block be less than 1mb? </p>

<p>To my understanding, a miner receives broadcasts. However, if not enough transactions come in, then would it just prematurely hash the block? </p>

CC BY-SA 3.0
2015-11-02T11:31:27.350Z
What do you mean by "prematurely"? Most miners hash every second they possibly can, otherwise their mining power is wasted.
David Schwartz
<blockchain><block><blocksize>
Can a Bitcoin block be less than 1mb?
jxieeducation
# Can a Bitcoin block be less than 1mb?

(Asked by: username_0 on 2015-11-01)

Can a Bitcoin block be less than 1mb?

To my understanding, a miner receives broadcasts. However, if not enough transactions come in, then would it just prematurely hash the block?

**Tags:** blockchain, block, blocksize

> **Comments:**
> **username_1**: What do you mean by "prematurely"? Most miners hash every second they possibly can, otherwise their mining power is wasted.  

---

## 3 answers

### Answer by username_4 on 2015-11-01. Score: 8 | Accepted answer

Yes. Let's calculate the minimum size of a block:

* The [block header](https://bitcoin.org/en/developer-reference#block-headers) must be exactly 80 bytes. This is the only part of the block that miners actually mine; the rest of the block is data that the header securely references.
* The transaction count. This isn't part of the block header and it isn't part of the block data, but it's part of the peer-to-peer protocol [block message](https://bitcoin.org/en/developer-reference#block) so it gets counted towards the block size. For blocks with 253 or fewer transactions, this is 1 byte.
* The coinbase transaction, the only required transaction in a block. The coinbase transaction has the following fields with these minimum values:

  + 4 bytes -- version field
  + 1 byte -- number of inputs (always 1 for coinbase transactions)
  + 32 bytes -- [outpoint](https://bitcoin.org/en/developer-reference#outpoint) txid; always 32 0x00 bytes for coinbase transactions
  + 4 bytes -- outpoint index; always 4 0xff bytes for coinbase transactions
  + 1 byte -- number of bytes in coinbase field (input script); always 1 byte for coinbase transactions because there's a 100-byte limit
  + 4 bytes -- block height as a data push; required by [BIP34](https://github.com/bitcoin/bips/blob/master/bip-0034.mediawiki)
  + 4 bytes -- [sequence number](https://bitcoin.org/en/developer-guide#locktime-and-sequence-number)
  + 1 byte -- number of outputs, we're not going to have any (making the block reward and transaction fees paid in this block permanently unspendable; no real miner would do this)
  + 4 bytes -- [locktime](https://bitcoin.org/en/developer-guide#locktime-and-sequence-number)
  + **Total:** 55 bytes

**Total minimum block size:** 80 + 1 + 55 = 136 bytes

Practically, the smallest reasonable blocks are in the 180-byte range.

> **Comments:**
> **username_5**: Empty `vout` would make the transaction [invalid](https://github.com/bitcoin/bitcoin/blob/master/src/main.cpp#L725-L726). You would need to have one output of 0 BTC, 0 length, null script for a total 9 bytes (8 byte value, one byte VarInt). This would also be an anyone can spend output as a null script can be satisfied by pushing anything to the stack.  

---

### Answer by username_2 on 2015-11-01. Score: 0

Sure.

[This](https://blockchain.info/block/00000000000000000fc5e782386b679ad5833ea2cddf4e06ebb403d725655a69) is one such block. It's 312 kB.


---

### Answer by username_3 on 2015-11-02. Score: 0

Blocks have to have at least one transaction: They must contain a coinbase which is the transaction that spends the block reward.

For example this [block with only one transaction](https://blockchain.info/block-index/512049/00000000000000000429a0c4fbe735b2d8b493daedf0207728543f748c262437) is only `0.246 kB`.


---

