user129599: I've heard there are somewhere in the range of 80-100 million possible UTXOs, where users could hold their own keys, with their BTC savings inside, and still have them spendable in the future.
Best answers would factor all limits including:

BTC believed to be lost forever
existing dust limit
existing block size limit over time (how long would it take to saturate all possible UTXOs)
A reasonable amount of sats within the UTXO higher than the dust limit to then send.
Any other possible restricting factors on resources that might limit total userbase holding their own keys.


user5406: There are currently already about 84.3M UTXOs. The consensus rules don't restrict the UTXO set size except that the UTXO set growth is delimited by the available blockspace. The smallest output type is P2WPKH with 31 vB. It would be possible to create about 32k P2WPKH outputs per block. At about 52,600 blocks per year, it would be possible to create about 1.68B P2WPKH UTXOs per year, if we put our blockspace almost exclusively toward that.
The output type with the smallest input weight is P2TR. A P2TR input weighs 230 WU (57.5 vB). Let's assume that we do not want to pay more than 1% in fees to spend a UTXO. At the minimum relay feerate of 0.25 s/WU (1 s/vB), a UTXO would need to hold at least 5,750 sats so that spending it wouldn't cost more than 1%  of its value. This is already more than the dust limit.
The current supply at block 757,069 is 19,166,364.05747152 BTC. Using the very small lower bound of 5,750 sats from above and assuming no bitcoins lost, we could create about 333B UTXOs.
Let's assume more reasonable numbers:

20% of all bitcoins, 3.83M have already been lost, leaving about 15.3M
“Useful” UTXOs are at least 20,000 sats
Both inputs and outputs are of the same type: P2TR (input 57.5 vB, output 43 vB)

Per these numbers, we could have 76,500,000,000 “useful” UTXOs. We can create about a maximum of about 23k P2TR outputs per block which translates to about 1.2B UTXOs per year. It would take over 63 years to create the maximum count of “useful” UTXOs, with only minimal other block activity beside creating UTXOs.
Let's assume instead that people are also using the blockchain for actual transaction activity, but the average transaction is a 1-input-5-output P2TR transaction, increasing the input-output ratio significantly compared to today. We can fit about 3,500 such transactions into a block, increasing the UTXO count by 14k per block. Now it would take about 104 years to reach the 76.5B count of UTXOs with 20,000 sats.
However, if we were just trying to get to one UTXO per person on the planet, we could get there in about 11 years per the 1-input-5-output P2TR transactions. Even this would increase the UTXO set size on the order of two magnitudes, making it more difficult to run a node at home.

129599: <p>I've heard there are somewhere in the range of 80-100 million possible UTXOs, where users could hold their own keys, with their BTC savings inside, and still have them spendable in the future.</p>
<p>Best answers would factor all limits including:</p>
<ul>
<li>BTC believed to be lost forever</li>
<li>existing dust limit</li>
<li>existing block size limit over time (how long would it take to saturate all possible UTXOs)</li>
<li>A reasonable amount of sats within the UTXO higher than the dust limit to then send.</li>
<li>Any other possible restricting factors on resources that might limit total userbase holding their own keys.</li>
</ul>
 5406: <p>There are currently already about 84.3M UTXOs. The consensus rules don't restrict the UTXO set size except that the UTXO set growth is delimited by the available blockspace. The smallest output type is P2WPKH with 31 vB. It would be possible to create about 32k P2WPKH outputs per block. At about 52,600 blocks per year, it would be possible to create about 1.68B P2WPKH UTXOs per year, if we put our blockspace almost exclusively toward that.</p>
<p>The output type with the smallest input weight is P2TR. A P2TR input weighs 230 WU (57.5 vB). Let's assume that we do not want to pay more than 1% in fees to spend a UTXO. At the minimum relay feerate of 0.25 s/WU (1 s/vB), a UTXO would need to hold at least 5,750 sats so that spending it wouldn't cost more than 1%  of its value. This is already more than the dust limit.</p>
<p>The current supply at block 757,069 is 19,166,364.05747152 BTC. Using the very small lower bound of 5,750 sats from above and assuming no bitcoins lost, we could create about 333B UTXOs.</p>
<p>Let's assume more reasonable numbers:</p>
<ul>
<li>20% of all bitcoins, 3.83M have already been lost, leaving about 15.3M</li>
<li>“Useful” UTXOs are at least 20,000 sats</li>
<li>Both inputs and outputs are of the same type: P2TR (input 57.5 vB, output 43 vB)</li>
</ul>
<p>Per these numbers, we could have 76,500,000,000 “useful” UTXOs. We can create about a maximum of about 23k P2TR outputs per block which translates to about 1.2B UTXOs per year. It would take over 63 years to create the maximum count of “useful” UTXOs, with only minimal other block activity beside creating UTXOs.</p>
<p>Let's assume instead that people are also using the blockchain for actual transaction activity, but the average transaction is a 1-input-5-output P2TR transaction, increasing the input-output ratio significantly compared to today. We can fit about 3,500 such transactions into a block, increasing the UTXO count by 14k per block. Now it would take about 104 years to reach the 76.5B count of UTXOs with 20,000 sats.</p>
<p>However, if we were just trying to get to one UTXO per person on the planet, we could get there in about 11 years per the 1-input-5-output P2TR transactions. Even this would increase the UTXO set size on the order of two magnitudes, making it more difficult to run a node at home.</p>
