Give SQL Server room.
Keep your server breathing.

An estimate you can inspect.

This calculator follows a conservative planning model inspired by Microsoft’s memory configuration guidance. Its defaults and equal instance split are tool assumptions, not an official Microsoft recommendation for your server.

The calculation

Subtract the OS reserve, other applications and all instance thread-stack reserves from physical memory. Allocate 75% of the remainder, split equally across instances, then round down to whole MB. The remaining 25% is headroom for allocations outside the setting.

per instance = floor((RAM − OS − apps − stacks × instances) × 0.75 × 1024 / instances)

Edition awareness

For 2017–2022, Standard’s buffer-pool limit is 128 GiB and Express’s is 1,410 MB. These are not total process-memory limits. The tool flags estimates above these limits rather than treating them as a cap on every SQL allocation. Developer is for non-production use.

After making a change

Capture the current setting before applying changes. Monitor Windows Available MBytes, paging, SQL process memory, memory grants and workload latency. SQL Server can allocate memory outside max server memory. Rebalance instances using observed peak demand; an equal split may not fit different workloads.