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How Bitcoin Fees Work: A Data-Driven Guide

· One min read
OverBlock Team
OverBlock Team
OverBlock Engineering

Bitcoin transaction fees confuse even experienced developers. They fluctuate wildly, different services give different estimates, and getting them wrong costs real money.

The basics: fee rate, not fee amount​

Bitcoin transactions compete for block space based on fee rate in sat/vB. Higher fee rate = faster confirmation, regardless of the amount being sent.

Why the mempool drives everything​

The mempool is the queue of unconfirmed transactions waiting to be mined. During high demand — popular NFT mints, market volatility, Ordinals activity — you may need 50+ sat/vB for the next block.

Provider comparison​

mempool.space, bitcoiner.info, and blockstream all implement fee estimation differently. At OverBlock we track what each provider recommended and whether it actually got into the next block, stored as BlockEval per confirmed block.

Using the OverBlock Fee API​

# Last 6 hours of block evaluations
curl "https://overblock.io/api/fees/history?windowMs=21600000"

# Latest block evaluation
curl "https://overblock.io/api/fees/latest"

See the fee advisor docs for the full reference.