# Inscription Estimates To guarantee the safety of user funds, a watchtower/validator inscribes the state difference to bitcoin as a refundTx to safeguard user funds in case of liveness failure. This ensure the data availability of refund is guaranteed by the bitcoin blocks itself, ie. It uses bitcoin as a data availability layer to commit state difference transaction. **Some points to consider:** 1. Inscription size of RefundTx is largely depended on number of accounts in the system = number of refund outputs. 2. Every refund output in the refundTx adds \~30vbytes 3. The size of the compressed refundTx can change based on ratio of compression. 4. The 4 byte identifier reduces the output size by 26 bytes per address. 5. Estimated fees in USD changes with BTC price and network fee rate. Calculations below assumes 36 sats/byte for the calculations. BTC/USD price and current fee rate in the network are variable parameters and will change fee in USD numbers. 6. This document assumes a bull case for Bitcoin. Assumptions may be different for a bear case. **What we don’t consider:** 1\. Consuming more than half the block space by other L2 projects will create fee pressure in the system, leading to much higher sats/byte | Number of refund Output | Inscription Size (vBytes) | Fee in Sats @
36 sats/byte | Fee in USD 
@ BTC = \~$65,500 | Inscription Size (bytes) with 4 byte identifier | Fee in Sats with 4 byte identifier @ 36 sats/byte | Fee in USD with 4 byte identifier @ BTC = \~$65,500 | Fees in USD with 4 byte identifier @ BTC = $100,000 , 36 sats/byte | Fees in USD with 4 byte identifier @ BTC = $100,000, 50 sats/byte | | ----------------------- | ------------------------- | -------------------------- | ----------------------------- | ----------------------------------------------- | ------------------------------------------------- | --------------------------------------------------- | ------------------------------------------------------------------ | ----------------------------------------------------------------- | | 1 | 600 | 21600 | 14 | 585 | 21060 | 14 | 21 | 29 | | 100 | 2760 | 99360 | 65 | 2748 | 98938 | 53 | 99 | 137 | | 250 | 6015 | 216540 | 142 | 4768 | 171648 | 113 | 171 | 239 | | 500 | 12015 | 432540 | 284 | 8970 | 322920 | 212 | 323 | 448 | | 750 | 18866 | 679176 | 445 | 13170 | 474120 | 311 | 474 | 658 | | 1000 | 24291 | 874476 | 572 | 17370 | 625320 | 411 | 625 | 868 | For \~ 100 bitcoin blocks a day, we assume 100 inscriptions committing a state difference. Per day cost of inscriptions for 100 inscriptions a day \~ $ 411 \* 100 = $41,100 Per month cost if BTC/USD price remains the same = $41,100 \*30 = $1,233,000 6 month estimate if price remains the same = $7,398,000 6 month estimate with BTC @ $100k and fee rate @ 36 sats/byte = $11,255,760 6 month estimate if fee rate rises to 50 sats/byte with BTC @100k = $15,633,000