In this article
Board size is one of the few governance decisions that shapes everything else a board does, from how fast it decides and how deeply it can examine an issue to whether it has room for the expertise it actually needs. S&P 500 boards now average 10.7 directors, but the right number for any given organization depends on its committee structure, regulatory exposure and stage of growth.
Shifts in regulatory expectations and the increased importance of independence and board diversity make board size worth revisiting on a regular cycle.
This guide covers what determines the right board size and how to change it:
The most cited evidence for smaller boards is a 2014 analysis that is now more than a decade old, produced by a firm that no longer exists independently. Newer research reaches a more nuanced conclusion.
A 2026 meta-analysis in Corporate Governance pooled 346 studies across 110 countries and found that the relationship between board size and performance depends on context. Larger boards bring more resources but carry higher coordination costs, and which force dominates varies. Where the drag appears, it shows up in market-based measures such as share returns rather than accounting measures such as return on assets, and it has grown more pronounced in recent studies and at larger firms. Regulated industries are one such context. Banking institutions face heavier scrutiny than other businesses and often need multiple committees, which keeps larger boards defensible in financial services.
The practical number has barely moved. Main Data Group found the median Russell 3000 board held at roughly ten directors from 2017 through 2024, even as governance responsibilities expanded. The Spencer Stuart Board Index, now in its 40th edition, puts the S&P 500 average at 10.7 directors, ranging from six to 18, with 77% falling in the nine- to 12-director band.
Boards are absorbing more complexity without adding seats.
A board should be large enough to carry out its fiduciary and other duties effectively and efficiently. For many organizations, that means five to seven directors. Up to 15 directors is workable at the high end to account for unusual circumstances.
Depending on the type of organization, boards should weigh several factors when setting their size:
Adding seats to acquire a single capability carries its own cost.
"Real estate on a board is very limited. You want some expertise, but you want a well-rounded board. If you have an expert on the board in one area, they become the person to handle that and the rest of the board tunes out. So it's incumbent on boards and the nom/gov committee to think critically and look at their own boards like an activist does. What are the strategic needs of our boards now? What about in three years, five years? Are we purpose-built? If not, need to start the recruiting process," says Jon Solorzano, Counsel, Environmental, Social and Governance at Vinson & Elkins, from the Diligent Elevate 2024 conference.
Legal requirements set the outer bounds before any of these considerations apply. State law sets the floor, and the organization's bylaws set the authorized range above it. Best practice is to specify a range in the bylaws rather than a fixed number. That lets the board adjust as directors join or depart without a formal amendment.
Committee staffing sets a practical minimum. Boards must be large enough to staff the audit, compensation and nominating/governance committees that listing standards require. An undersized board risks directors being unable to fulfill both their board and committee duties effectively.
Lifecycle stage matters too. Early-stage organizations typically start with five to seven directors and expand as complexity grows. Established organizations running multiple standing committees generally need more seats, in line with the nine- to 12-director band where most large-cap boards sit.
Whatever size a board settles on, its composition should match the oversight challenges it has identified. Current data suggests many boards fall short here. According to What Directors Think 2026 by Diligent Institute and Corporate Board Member, 40% of directors named technological developments, including AI, as the single most challenging issue to oversee. Only 8% rate their board as having strong AI expertise, the lowest score across every area surveyed.
Skills matrices identify these gaps. Recruitment and director education close them. Adding a non-fiduciary advisory board is another route to expertise without expanding the fiduciary board.
A board skills matrix shows which capabilities your directors already cover and where recruitment should focus.
Size changes how a board behaves. The trade-offs run in both directions.
Fewer voices in the room does not automatically produce better debate. Boards of any size have to make room for disagreement deliberately.
"How do you encourage respectful dissent? Instead of asking, 'Do we agree?' ask 'What's missing?'" says Lori Nishiura Mackenzie, Co-Founder of the Stanford VMware Women's Leadership Innovation Lab, also from our Elevate 2024 conference (cited previously).
Smaller boards place more work on each director, which reduces effectiveness if directors cannot commit the time. Lower numbers may also leave too few directors to staff required committees. And with fewer seats, there is less room for the range of backgrounds and perspectives that stakeholders now expect.
Typical board size differs by organization type and scale, so benchmark against your own peer group. No single universal number applies.
| Organization type | Average board size | Source and date |
|---|---|---|
| S&P 500 companies | 10.7 directors | 2025 U.S. Spencer Stuart Board Index |
| S&P MidCap 400 companies | 9.8 directors, unchanged from 2024 | MidCap Board Index, December 2025 |
| Nonprofits (historical benchmark) | 15 directors | Leading with Intent 2017, BoardSource |
The nonprofit figure is explicitly historical. BoardSource's 2026 survey is open but unpublished, so 15 directors remains the last confirmed published average.
See how leading boards structure composition, independence and committee coverage as they scale.
Board size should be reviewed on a set cycle rather than only in response to a crisis. The nominating and governance committee typically leads that review, and board self-assessments are where size and composition questions usually surface first.
"The board needs to be a living and breathing entity. Be fluid and often reassess the board to identify where you have gaps in skills and diversity and thought," says Lee Anne Sexton, Managing Director at Donnelley Financial Solutions.
Four triggers should prompt a review:
In November 2017, GE announced plans to cut its board from 18 directors to 12, retiring nine sitting directors and adding three with relevant industry experience. The company adopted a 15-year cap on director terms and engaged a search firm to find candidates with expertise in aviation, power, healthcare and digital manufacturing.
The reduction took effect with the 2018 proxy slate. By the 2019 annual meeting the board had gone to ten, after its two longest-tenured directors, Geoff Beattie and Jim Mulva, retired and two new directors joined the slate. Across two years, 15 directors left and seven arrived, leaving an average tenure of 2.5 years.
GE also asked shareholders to amend its Certificate of Incorporation to lower the minimum required number of directors from ten to seven. That was a floor rather than a target. GE's 2019 proxy stated that the board expected to keep targeting a size of approximately 12 directors.
GE's reduction rested on a judgment about which seats were earning their place.
"Long-tenured boards are perceived to no longer be fully independent. But the counter-argument is the board has been through multiple cycles and multiple CEOs. On the flip side, having a totally new board isn't ideal either. There's no institutional memory. You need to find the right balance of tenure. Have some more senior directors and some newer directors with fresh ideas," says Solorzano.
Two problems recur throughout this guide. One is knowing what size and composition your peer group actually runs. The other is making sure a leaner board can still absorb the workload without overloading individual directors.
Diligent Market Intelligence addresses the first. Its governance benchmarking covers board structure, composition and practices across a large body of public company data, so a nominating and governance committee can test a proposed size against what peers and institutional investors actually accept rather than against a general rule of thumb. For public companies, the same dataset supports proxy season planning and shareholder engagement using historical voting patterns.
Diligent Boards addresses the second. Smaller boards concentrate more work on each director, and that pressure lands hardest on preparation. Smart Builder creates first drafts of board books and committee materials from existing content, which reduces the manual compilation that consumes corporate secretary time. Smart Risk Scanner reviews materials for risky language and legal red flags before they reach directors. Action Tracker converts meeting notes into trackable items so follow-through does not depend on a larger board to distribute it across.
Together these address the two constraints a resizing decision runs into: whether the number is defensible to investors, and whether the directors you keep can carry the load.
There is no single ideal, but the ranges cluster tightly. Most large-cap public boards sit between nine and 12 directors, with S&P 500 boards averaging 10.7 according to Spencer Stuart. Smaller and early-stage organizations commonly run five to seven. The right number is the smallest board that can staff its required committees, cover the expertise its oversight agenda demands and maintain independence.
The research points in two directions, and both findings warrant consideration. Bain and Company research found that once a decision-making group reaches seven people, each additional member reduces decision effectiveness by 10%. BoardSource's 2007 Nonprofit Governance Index found that boards with 15 to 22 directors were rated more effective by their chief executives and reported better governance practices. Smaller boards decide faster. Larger nonprofit boards spread fundraising and committee duties across more people while broadening representation. A nonprofit board composition matrix helps determine which of those your organization needs most.
It depends on the state and the type of entity. For for-profit corporations, Delaware General Corporation Law §141(b) permits a board of one or more directors. For nonprofits, state minimums are usually two or three directors; Illinois requires three under 805 ILCS 105/108.10(a). For 501(c)(3) organizations, IRS guidance informally expects at least three unrelated directors, and applications may be rejected where board independence cannot be demonstrated. No statute or regulation states a three-director rule.
No. Boards may have either an odd or even number of directors, though odd numbers are common practice. BoardSource notes that ties can be managed by the chair, who can either abstain or cast a determining vote. A 50/50 split can also be a useful signal. BoardSource's board meetings guidance suggests a tie vote may indicate an issue that needs further discussion, and that tabling it until the next meeting allows for additional data gathering.
Current composition trends favor fewer directors and greater independence. Industry and organizational need should determine the final number, and that number should change when the organization does. The practical test is asking "Can this board staff its committees, cover its oversight agenda and still hold a real discussion?"
Ready to build a board structure your investors can defend? Request a demo to see Diligent in action and sign up for the Boards and Governance newsletter from Diligent for updates on board composition and governance.
