There's no single "correct" Bitcoin fee. The right rate in sat/vB depends entirely on how busy the mempool is at the moment you hit send. Here's how to read the low/medium/high recommendations, when 1-2 sat/vB is plenty, and when it pays to spend a little more.
What sat/vB actually means
Bitcoin fees aren't priced per transaction or per dollar sent, they're priced by size. The unit is satoshis per virtual byte, written sat/vB. A satoshi is one hundred-millionth of a bitcoin, and a virtual byte ("vbyte") measures how much space your transaction takes up in a block.
So your total fee is roughly your transaction's size in vbytes × the sat/vB rate you choose. A simple payment might be around 140 vBytes; a transaction that sweeps many small inputs can be far larger. That's why two people sending the same amount of bitcoin can pay very different fees, the fee follows the data footprint, not the value. Miners order the mempool by sat/vB and fill each block with the highest-paying transactions first, which is the whole reason this single number matters so much.
How the low / medium / high recommendations work
Most fee trackers, including Bitcoin Insight, show three suggested rates. They're estimates of what it takes to get confirmed within a certain number of blocks, based on what's currently waiting in the mempool:
- High priority, aims for the very next block or two (roughly 10-20 minutes). Use it when timing genuinely matters.
- Medium priority, targets confirmation within about half an hour to an hour. A sensible default for most payments.
- Low priority, the economical rate. It may take several blocks or longer, but it's the cheapest way to get on chain.
These are forecasts, not guarantees. They shift as the mempool fills and empties, so a "high" rate at 2am can be lower than a "low" rate during a busy afternoon. Always read them live rather than memorizing a number.
Why the right fee depends on mempool congestion
Bitcoin produces a new block roughly every 10 minutes, and each block has limited space. When fewer transactions are waiting than blocks can clear, there's no competition and fees fall toward the network minimum. When more transactions pile up than blocks can absorb, senders bid against each other and the going rate climbs.
That backlog is the mempool. Watching it is the single best way to judge fees: a near-empty mempool means you can pay a few sat/vB and still confirm quickly, while a deep backlog means the low rate might take hours. If you understand the mempool, you understand fees, they're two views of the same thing.
How to avoid overpaying
Overpaying usually comes from guessing instead of checking. A few habits keep fees low:
- Check before you send. Glance at the live rates and the fee chart's trend. If fees are falling, waiting an hour can halve your cost.
- Match the fee to the urgency. Moving savings to cold storage rarely needs high priority, the low rate is fine.
- Send when the mempool is quiet. Evenings and weekends are often calmer. There's no fixed schedule, which is exactly why a live tracker helps.
- Don't trust your wallet's default blindly. Some wallets pad the estimate. If you know the live rate, you can set it yourself with confidence.
When 1-2 sat/vB is fine, and RBF in brief
Paying just 1-2 sat/vB is perfectly reasonable when the mempool is nearly empty and you're not in a rush, for example, consolidating inputs or topping up cold storage overnight. The risk is that congestion can return before your transaction confirms, leaving it stuck.
That's where Replace-By-Fee (RBF) comes in. If you flag a transaction as replaceable when you send it, you can later broadcast a new version of the same transaction with a higher fee to jump the queue. So a smart low-fee strategy is: send at a low rate with RBF enabled, watch the mempool, and bump only if it stalls. You get the cheap path most of the time and an escape hatch when you need it.
How to track Bitcoin fees live on iPhone
The cleanest way to check fees on iPhone is a native Bitcoin transaction fee app rather than a browser tab. Bitcoin Insight is built for exactly this:
- Live fee tracker, current low, medium and high sat/vB rates on the dashboard, updating in real time from the public mempool.space API.
- Fee chart, a finger-scrubbable history so you can see whether rates are climbing or cooling off before you send.
- Home & Lock Screen widgets, keep the current fee in view at a glance, no app launch required.
- The full picture, mempool size, block height and a built-in block explorer alongside the fees, so you can confirm why the rate is what it is.
It's a native iOS app (iOS 17+), free and open source under the MIT license, with no accounts, no ads and no tracking, the only paid extra is a one-time unlock for the widgets. If you want to compare options first, see the best Bitcoin mempool apps for iPhone.
FAQ
What is a good Bitcoin fee in sat/vB right now?
It depends on how busy the mempool is. When the network is quiet, 1-5 sat/vB often confirms within a few blocks, and 1 sat/vB can be enough if you are not in a hurry. When the mempool is congested, the high-priority rate can climb to dozens or even hundreds of sat/vB. The only reliable answer is the live rate, so check a fee tracker before you send rather than trusting a fixed number.
How do I check Bitcoin fees on my iPhone?
Open a native fee tracker like Bitcoin Insight. Its live dashboard shows the current low, medium and high fee recommendations in sat/vB, plus a fee chart so you can see whether rates are rising or falling. You can also add a Home or Lock Screen widget to keep the current fee in view without opening the app.
Is 1 sat/vB enough to send Bitcoin?
Sometimes. When the mempool is nearly empty, a 1 sat/vB transaction can confirm in the next few blocks. When the mempool is busy, a 1 sat/vB transaction may sit unconfirmed for hours or days, or get dropped. If you might need it sooner, send with RBF enabled so you can bump the fee later, or pay the current low rate instead.