How do you estimate support resources for the Project Manager as our role expands?

Francisco, I think your question reveals an important tension in how the Project Manager role is evolving.

If approaches such as M.O.R.E. expand what PMs are expected to own, from delivery toward broader perspective, adaptability, outcomes and value, I would hesitate to solve the resulting capacity problem simply by adding support around the PM. We should first ask a more fundamental question: as the role expands, what should stop being the PM’s work?

Before estimating coordinators, analysts or administrative support, I would decompose the work.
What can be eliminated, simplified or automated?
What should remain with the people closest to the work?
What belongs to other organizational roles? And what genuinely requires the PM’s integration, judgment and engagement with governance?

Otherwise, we risk creating role accumulation rather than role evolution: broader strategic expectations layered on top of the existing workload, supported by an expanding structure around the PM.

So I would not start with budget, team size or any single complexity proxy.
I would start with work design, decision rights and authority.
Only then would I estimate support capacity from the volume, variability and complexity of the work that legitimately remains.

New expectations for Project Managers should trigger a redesign of how project work is distributed, not simply an expansion of the structure required to support the existing model.

I think workload visibility has to come before deciding whether additional support is needed. Team size alone doesn’t always tell the full story, especially when the PM and supporting resources are spread across multiple projects.
I’ve found tools like KolApp useful for this because you can look at workload and capacity across projects rather than relying only on headcount. It makes it easier to see whether someone is genuinely overloaded or whether the work can be redistributed before adding another resource.

I don’t use a fixed rule based only on budget or team size. I look more at the amount of coordination the project requires: number of stakeholders, dependencies, reporting needs, governance, vendors, and how much administrative work the PM is carrying.

If those activities are taking a significant part of the PM’s time away from decisions, risks, stakeholders, and delivery, that is usually a good indication that additional support is needed.

In my experience, this varies a lot by organization, and I've seen both extremes. Some companies overstaff — I've worked in places with a large PMO bench where the number of running projects didn't come close to justifying the headcount, and it just added overhead without much value. Others deliberately understaff, keeping the team leaner than they probably should to control costs, and it shows in strain on the PMs.

Two patterns I've actually seen work as triggers for adding support:

Reactive, incident-driven staffing: Specific shortcomings — things that slipped or went unmonitored because there wasn't enough PM or BA bandwidth — get reported up to the executive committee, and that failure becomes the justification to hire.

Proactive portfolio-based planning: An annual portfolio review estimates the total project volume and the average capacity per PM (hours or number of projects each can realistically manage), then sizes headcount against projected growth — e.g., "portfolio grows 20% next year, so we need two more PMs on top of backfills."

Bottom line: there's no single reliable rule of thumb (budget, team size, complexity) that works across companies. It really comes down to organizational maturity and whether staffing is driven reactively by visible failures or proactively by portfolio capacity planning.