Why Does Transaction Size (vByte) Differ Between Blockstream Green and BlueWallet?

I am testing two mobile wallets, Blockstream Green and BlueWallet, and noticed differences in transaction fees for identical transactions, even when the fee rate (sat/vByte) is set the same. Background on My Setup and Transactions Imported the same seed phrase into both wallets. My wallet contains only one UTXO. Sending the entire balance to another address using either Green or BlueWallet. Both sending and receiving addresses start with "bc1" (SegWit/Bech32/P2WPKH address). Fee rate is set at 1 sat/vByte for simplicity. Observations: Performing identical transactions in both wallets shows differences in calculated transaction size: Green wallet: 177 vByte (screenshot A.1). BlueWallet: 340 vByte (screenshot A.2). TLDR1: Q1. Why does the same transaction (from one UTXO) result in different transaction sizes (and therefore fees) between the two wallets (A.1 vs A.2)? Additional Findings (Green wallet): I noticed larger calculated transaction sizes with higher sending amounts: Sending 0.10001000 BTC: 141 vByte (screenshot B.1). Sending 0.10001001 BTC: 208 vByte (screenshot B.2). Note: The sole UTXO exceeds these amounts. TLDR2: Q2. Why does adding just 1 satoshi increase the transaction size significantly (B.1 vs B.2)? Aren’t both transactions considered 1-input 2-outputs? Q3. Interestingly, sending the whole balance results in 177 vByte (A.1), which is a 1-input 1-output transaction, yet the size is between the two 1-input 2-outputs transactions above, any idea why? Comparison with BitcoinOps: According to BitcoinOps: A 1-input 1-output P2WPKH transaction = ~109.5 vByte. A 1-input 2-output P2WPKH transaction = ~140.5 vByte (+31 vByte). TLDR3: Q4. Why does Green wallet's calculated transaction size differ from BitcoinOps' suggested size? Lots of questions here, but any insights on any one of them would be greatly appreciated. Thanks in advance! submitted by /u/Typical9Veg [link] [comments]

Mar 16, 2025 - 06:13

I am testing two mobile wallets, Blockstream Green and BlueWallet, and noticed differences in transaction fees for identical transactions, even when the fee rate (sat/vByte) is set the same.

Background on My Setup and Transactions

Imported the same seed phrase into both wallets.
My wallet contains only one UTXO.
Sending the entire balance to another address using either Green or BlueWallet.
Both sending and receiving addresses start with "bc1" (SegWit/Bech32/P2WPKH address).
Fee rate is set at 1 sat/vByte for simplicity.

Observations:

Performing identical transactions in both wallets shows differences in calculated transaction size:

Green wallet: 177 vByte (screenshot A.1).
BlueWallet: 340 vByte (screenshot A.2).

TLDR1:
Q1. Why does the same transaction (from one UTXO) result in different transaction sizes (and therefore fees) between the two wallets (A.1 vs A.2)?

Additional Findings (Green wallet):

I noticed larger calculated transaction sizes with higher sending amounts:

Sending 0.10001000 BTC: 141 vByte (screenshot B.1).
Sending 0.10001001 BTC: 208 vByte (screenshot B.2).

Note: The sole UTXO exceeds these amounts.

TLDR2:
Q2. Why does adding just 1 satoshi increase the transaction size significantly (B.1 vs B.2)? Aren’t both transactions considered 1-input 2-outputs?
Q3. Interestingly, sending the whole balance results in 177 vByte (A.1), which is a 1-input 1-output transaction, yet the size is between the two 1-input 2-outputs transactions above, any idea why?