Fees and vsize

A fee is the part of the inputs that no output claims. The miner who includes the transaction collects it, on top of the new coins in the block reward.

Nothing in a transaction says “fee”. You find it by subtraction. And since block space is what’s scarce, fees are compared per unit of size: grains per virtual byte. This page explains both numbers and the limits around them.

Try it

Pick a transaction shape and a fee rate and see what it costs.

Fee calculator

Fee = fee rate × vsize, paid in grains

Fee rate grains / vB

vsize vbytes

Fee 0.00007854 PRL

7,854 grains

51 grains/vB × 154 vB.

Relay minimum: 1 grain/vB; below it, nodes don’t relay
Dust limit: 333 grains; smallest Taproot or P2MR output nodes relay
Typical rate: ~51 grains/vB; what payments paid in October 2026

Runs in your browser · nothing is sent src/lib/format.ts · real sizes from mainnet

Where is the fee?

In the gap between inputs and outputs. Take the real payment from block 130,825:

	Grains
Input: `33218153…:683`	495,654,555
Output 0 (change)	− 295,646,640
Output 1 (payment)	− 200,000,000
Fee	7,915

The input’s value isn’t in the transaction either; nodes look it up in the UTXO set. That’s why a node needs the outputs being spent before it can even tell what fee a transaction pays.

What is vsize?

A size in which witness bytes count a quarter. Pearl calls it virtual size, measured in vbytes:

\text{vsize} = \text{base size} + \left\lceil \frac{\text{witness size}}{4} \right\rceil

Base size is the transaction without marker, flag and witness: the bytes that make the txid.
Witness size is everything else: the marker and flag (2 bytes) plus all witness stacks.
The division rounds up, so even 1 to 3 witness bytes cost a full vbyte.

node/blockchain/vsize.go Go

func CalcVsize(baseSize int, witnessSize int) int64 {
	return int64(baseSize + (witnessSize+WitnessScaleFactor-1)/WitnessScaleFactor)
}

For the payment: 137 base bytes + ⌈68 ÷ 4⌉ = 137 + 17 = 154 vbytes, at 7,915 ÷ 154 = 51.4 grains per vbyte.

A typical payment: 1 input, 2 outputs 205 bytes

01000000 00 01 01 5939557091bae792be66f26cbd83fc78f16a690a854109e8a1d115e253812133 ab020000 00 ffffffff 02 b0359f1100000000 22 5120d7ab02c96a342bdddb5d07b9f3ebd6c04e077ff41418110b9a1e5997439416b2 00c2eb0b00000000 22 512062e9da3682aab288392cf7218bafc36287288abb3ce200c5d1a50aa234073b2b 01 40 4686c7014749649b25555874c7772ecb7a44e85454893ed5888db11ebcdc82a22d74ce1a1671d02810f5ba1dca3277409e95a653ba9644099f7da26be7a86ba2 00000000

Hover or focus the bytes to name each field Version bytes 0–3 1 Marker bytes 4 0x00 Flag bytes 5 0x01 Input count bytes 6 1 Previous txid bytes 7–38 33218153e215d1a1e80941850a696af178fc83bd6cf266be92e7ba9170553959 Output index bytes 39–42 683 scriptSig length bytes 43 0 Sequence bytes 44–47 0xffffffff Output count bytes 48 2 Amount bytes 49–56 295,646,640 grains (2.95646640 PRL) Script length bytes 57 34 Locking script bytes 58–91 prl1p674s9jt2xs4amk6aq7ul867kcp8qwll5zsvpzzu6revewsu5z6eqv9d5z4 Amount bytes 92–99 200,000,000 grains (2.00000000 PRL) Script length bytes 100 34 Locking script bytes 101–134 prl1pvt5a5d5z42egswfv7uscht7rv2rj3z4m8n3qp3w35592ydq88v4seuhn70 Witness items bytes 135 1 Schnorr signature length bytes 136 64 Schnorr signature bytes 137–200 4686c7014749649b25555874c7772ecb7a44e85454893ed5888db11ebcdc82a22d74ce1a1671d02810f5ba1dca3277409e95a653ba9644099f7da26be7a86ba2 Locktime bytes 201–204 0

Field	Bytes	Value
Version version	4 @0	1 int32 little-endian. Pearl wallets and pearld coinbases use version 1; relay policy accepts 1-2.
Marker marker	1 @4	0x00 Segwit marker (BIP-144): says witness data follows the outputs.
Flag flag	1 @5	0x01 Witness flag; 0x01 is the only value Pearl accepts.
Input count vin.length	1 @6	1 CompactSize number of inputs.
Previous txid vin[0].txid	32 @7	33218153e215d1a1e80941850a696af178fc83bd6cf266be92e7ba9170553959 The transaction being spent, stored byte-reversed (internal order); shown here in normal display order.
Output index vin[0].vout	4 @39	683 Which output of that transaction is spent (uint32 LE).
scriptSig length vin[0].scriptSig.length	1 @43	0 Always 0 for non-coinbase inputs in Pearl: every spend uses the witness instead.
Sequence vin[0].sequence	4 @44	0xffffffff Final (0xffffffff): no RBF signal, no relative locktime, and locktime is ignored for this input. Pearl wallets use this.
Output count vout.length	1 @48	2 CompactSize number of outputs.
Amount vout[0].value	8 @49	295,646,640 grains (2.95646640 PRL) int64 little-endian, in grains (1 PRL = 100,000,000 grains).
Script length vout[0].scriptPubKey.length	1 @57	34 CompactSize length of the locking script.
Locking script vout[0].scriptPubKey	34 @58	prl1p674s9jt2xs4amk6aq7ul867kcp8qwll5zsvpzzu6revewsu5z6eqv9d5z4 OP_1 OP_PUSHBYTES_32 <output key Q>: a Taproot output.
Amount vout[1].value	8 @92	200,000,000 grains (2.00000000 PRL) int64 little-endian, in grains (1 PRL = 100,000,000 grains).
Script length vout[1].scriptPubKey.length	1 @100	34 CompactSize length of the locking script.
Locking script vout[1].scriptPubKey	34 @101	prl1pvt5a5d5z42egswfv7uscht7rv2rj3z4m8n3qp3w35592ydq88v4seuhn70 OP_1 OP_PUSHBYTES_32 <output key Q>: a Taproot output.
Witness items witness[0].length	1 @135	1 Number of witness stack items for input 0.
Schnorr signature length witness[0][0].length	1 @136	64 CompactSize length of this witness item.
Schnorr signature witness[0][0]	64 @137	4686c7014749649b25555874c7772ecb7a44e85454893ed5888db11ebcdc82a22d74ce1a1671d02810f5ba1dca3277409e95a653ba9644099f7da26be7a86ba2 64-byte BIP-340 signature (R.x ‖ s) with SIGHASH_DEFAULT: a Taproot key-path spend.
Locktime locktime	4 @201	0 0: no time lock.

txid: d919e02a4adfd739ceef31d98803f0ddd24e1b1fa67b0fe572cdec42c1b384c9
Size: 205 bytes · 154 vbytes
Block: 130,825
Fee: 7,915 grains

The highlighted bytes, plus the 00 01 after the version, are the 68 discounted ones.

Real transactions, measured

Transaction	Size	Base	Witness	vsize	Fee	Rate
Payment, 1 in, 2 out	205	137	68	154	7,915	51.4
Payment, 2 in, 2 out	312	178	134	212	10,650	50.2
OP_RETURN, 1 in, 3 out	253	185	68	202	10,200	50.5
P2MR funding, 2 in, 2 out	312	178	134	212	10,803	51.0
P2MR 2-of-2 spend, 1 in, 3 out	387	180	207	232	1,000	4.3
Coinbase, block 130,825	216	180	36	189	none	–

Sizes in bytes, fees in grains, rates in grains per vbyte. The P2MR spend shows the discount at work: 207 bytes of witness, two signatures and a script, cost only 52 vbytes.

Why discount the witness?

Two reasons, both inherited from Bitcoin’s segwit:

Witness data can be dropped later. Once a block is deep in the chain, nodes don’t need old signatures to know the current set of coins. Base data, which defines that set, is the expensive part.
It makes spending cheaper than creating. Inputs carry witnesses; outputs don’t. Discounting witnesses nudges wallets to consolidate coins rather than fragment them.

How does a wallet know the size before signing?

Because every piece of a Pearl key-path spend has a fixed size. An input is 41 base bytes plus a 66-byte witness (count, length, 64-byte signature); a Taproot or P2MR output is 43 bytes; the rest is 10 bytes plus the 2-byte marker and flag. With n inputs and m outputs (under 253 of each):

\text{vsize} = 10 + 41n + 43m + \left\lceil \frac{2 + 66n}{4} \right\rceil

One input, two outputs: 10 + 41 + 86 + 17 = 154. Two and two: 10 + 82 + 86 + 34 = 212. Both match the real transactions in the table.

What’s the minimum fee?

1 grain per vbyte. Nodes won’t relay or mine a transaction paying less; the payment above would have needed at least 154 grains.

The code calls this DefaultMinRelayTxFee = 1000, “in Grain/1000 bytes”. Read “bytes” as vbytes: Pearl’s mempool computes every fee rate as fee × 1,000 ÷ vsize, and so does the wallet. Two unit traps follow:

“Per kB” means per 1,000 vbytes, everywhere in Pearl’s node and wallet.
RPC fee arguments are in PRL, not grains. Oyster’s feerateperkb of 0.00001 PRL/kB = 1,000 grains per 1,000 vbytes = 1 grain per vbyte, which is oystercli’s default. The plain RPC send calls have no default: the caller must pass a rate.

What do transactions actually pay?

A snapshot, not advice. On 2026-10-20 Pearl’s Blockbook estimated, in PRL per 1,000 vbytes:

To confirm within	Estimate	Grains per vbyte
1 block	0.00051294	about 51.3
2 blocks	0.00002432	about 2.4
3 blocks	0.00001005	about 1.0
6, 12 or 25 blocks	0.00001	1.0 (the floor)

Most payments in recent blocks paid about 50 to 51 grains per vbyte, matching the 1-block estimate. Some paid far less and still confirmed: the P2MR spend above paid 4.3. More than half of recent blocks carried only their coinbase, so space is rarely short.

Remember that Pearl’s wallet doesn’t signal replace-by-fee, so its transactions can’t be replaced by a higher-fee version after sending.

How big can things get?

Block: 1,000,000 vB; certificate not counted
Standard transaction: 100,000 vB; relay policy
Any transaction: 1,000,000 vB; consensus
Minimum relay fee: 1 grain/vB; 1,000 grains per 1,000 vB
Dust (Taproot, P2MR): 333 grains; smallest relayed output
Unconfirmed chain: 25 txs; and 101,000 vB of ancestors

A block’s vsize counts its 108-byte header, its transactions and their witnesses (discounted), but not the ~60 KB proof certificate that travels with it. There’s also a floor: Pearl’s mempool rejects transactions whose base size is under 65 bytes.