mempool.space — Guide

.space is Bitcoin's most widely used open source blockchain explorer. This page explains all the elements you see when you open mempool.space.

Open mempool.space →

Block visualization

The horizontal row of blocks at the top of the page is the heart of mempool.space. The blocks are divided into two types, each with its own color:

Green blocks — Upcoming

Projected blocks that haven't been mined yet. The contents update continuously in real time as miners prioritize transactions.

Purple blocks — Confirmed

Blocks that have already been mined and added to the blockchain. Shows fee rate (sat/vB), time, and number of transactions.

💡 Each block shows: number of transactions, median fee (sat/vB), size (MB), and time.

Fee estimates

Below the block visualization, recommended fee levels are shown in satoshis per virtual byte (sat/vB). The higher the fee, the faster the confirmation.

High priority

Next block (~10 min) — Use for time-critical transactions. The most expensive choice.

Medium

1–3 blocks (~10–30 min) — Good for most normal transfers.

Low priority

Can take hours or days — A cheap option if you're not in a hurry.

No rush

Waits until the network is quiet — The lowest possible fee. Unpredictable waiting time.

⚠️ The estimates are guidance only — during busy periods the median fee can rise quickly. Always check the current block visualization for the precise figures.

Mempool statistics

Key figures about the network's current state:

Unconfirmed transactions

The total number of transactions waiting to be mined. A high number means the network is busy and fees are rising.

Memory Usage

How much memory the pending transactions take up. Max ~300 MB per node. When exceeded, cheap transactions are dropped.

Purging

When the mempool is full, transactions with fees that are too low are automatically dropped to free up space.

Difficulty Adjustment

Forecast for the change in mining difficulty. +% = blocks are mined faster than 10 min (difficulty rises). −% = blocks are mined slower (difficulty falls).

The search function

At the top of the page you can search for three types of data:

Transaction ID (TXID)

Find a specific transaction and see its status — whether it's waiting in the mempool or confirmed.

Bitcoin address

See the history and balance of any Bitcoin address.

Block hash or block number

Explore the contents of a specific block and see all the transactions in it.

Networks and navigation

Via the dropdown menu in the top left (the Bitcoin logo), you can switch between four networks:

Mainnet

The real Bitcoin network. This is where all real transactions with real value take place.

Signet

A controlled test network with centrally managed blocks. More stable than Testnet — used by developers to test software.

Testnet3

The older public test network. Coins have no real value. Used to try out transactions without risk.

Testnet4

The newest generation of Bitcoin's public test network. Gradually replacing Testnet3 for developers.

Settings (footer)

At the top of the footer you'll find a number of dropdown menus to customize the display:

Language

Change the language of the whole site. Danish is available.

Currency

Choose which fiat currency amounts and fees are shown in — e.g. USD, EUR, or DKK.

Time zone

Adjust the time zone so block timestamps match your local time.

Unit

Choose whether amounts are shown in BTC or sats (satoshis).

Theme

Change the visual theme. "wiz" is a popular community theme with extra details.

Log in

Create an account to save settings, use the Accelerator, and get access to extra features.

Mempool Accelerator

Have you sent a transaction with too low a fee that's now stuck? Mempool Accelerator lets you pay a premium to push the transaction forward in the queue and get it confirmed faster. Find the feature directly on the front page or under the specific transaction.

Open Mempool Accelerator →

Glossary — key terms

sat/vB

Satoshis per virtual byte — the unit for Bitcoin transaction fees. Used to indicate how much you pay miners to process your transaction.

TXID

Transaction ID — a unique 64-character identifier for any Bitcoin transaction.

Confirmation

The number of blocks mined on top of the block that contains your transaction. More confirmations = greater security.

UTXO

Unspent Transaction Output — the "change" system Bitcoin uses. Your "balance" is the sum of all your UTXOs.

RBF

Replace-By-Fee — the ability to replace a pending transaction with a new one with a higher fee to speed up confirmation.

Sats / Satoshis

The smallest unit of Bitcoin. 1 BTC = 100,000,000 satoshis.

vByte

Virtual byte — a unit for measuring transaction size that accounts for the SegWit discount.

SegWit

Segregated Witness — a Bitcoin upgrade that separates signature data from transaction data. It introduced vBytes as a unit, where signature data is weighted lower — which reduces fees for SegWit transactions.