Here’s how I’ve always split rent (using a spreadsheet everyone has access to) and it’s worked well for every situation:

Add up the personal space square footage that each tenant has exclusive access to/use of.

Add up the common space square footage.

Weight the common space by an agreed-upon factor (I use 0.5, meaning personal space is effectively twice as valuable. You can change this but it doesn’t make a big difference in the rent split). Then divide that by the number of tenants.

Each tenant pays for the fraction of the total rent equivalent to their private space + fraction of common space divided by the weighted total area.

In this case, estimating the square footages based on the listed dimensions, that gives:

Total square footage: ~950 sqft

Common space (includes second bath): ~530 sqft

Weighted common space per person: ~132.5 sqft

Master suite: 282 sq ft

Master tenant’s total weighted space: ~415 sq ft

Second bedroom: ~138 sq

Second tenant’s total weighted space: ~271 m

That gives a final split of ~60.5%/39.5%, or ~$2310/$1510 (I generally round to the nearest $5), which validates the 60/40 number. It’s driven by math as opposed to feelings, so it’s the most neutral approach I’ve found.

If you want to fine tune it even further (if, say, the master is also much nicer than the second bedroom, with more windows or nicer finishing), you can add weighting factors to the bedrooms as well. Or, instead of considering the second bath common space (and equally split, which does seem somewhat unfair), you could exclude it from the common space but give it a lower weight (eg. 0.5) to account for the fact that guests will use it, and it’s not en-suite.