Optimal HR Staffing Levels: What ADP Research Shows

There is no single ideal HR-to-employee ratio, but ADP Research gives useful reference points. Its 2023 analysis of payroll data found HR staffing as a share of total staffing rose more than 10 percent since 2018, and lower HR staffing coincided with higher turnover, with diminishing returns. Use those findings as a starting point, then adjust for your workforce.

Key takeaways

  • ADP Research measures HR staffing as HR personnel per 100 employees.
  • ADP reported the average rising from 2.35 to 2.6 HR staff per 100 employees since 2018.
  • Very low HR staffing was associated with higher monthly turnover, but adding staff had diminishing benefits.
  • Small employers tend to have higher ratios because some HR work is fixed regardless of headcount.
  • Your right number depends on complexity, frontline mix, compliance load and technology, not a benchmark alone.

What did ADP Research find about HR staffing?

In "HR: How much is too much, or too little?" published in August 2023, ADP Research defined the HR staffing ratio as the number of HR personnel for every 100 employees and analyzed it using ADP payroll data going back to 2018. Key findings:

  • HR staffing grew. HR counts as a share of total staffing were up more than 10 percent since 2018.
  • Size matters. The smallest firms, with fewer than 50 workers, can average more than two HR staff per 100 employees, and their ratios rose 3.8 percent since 2018. Larger companies saw faster and steadier growth.
  • Frontline industries grew fastest. Ratios rose most in industries with large, lower-wage frontline workforces, though white-collar industries typically have higher ratios overall.
  • Recruiters drove some growth. Recruiters' share of HR staff grew over 26 percent from 2018 through April 2023, but that growth slowed sharply as hiring cooled.
  • Turnover link, not proof. Lower HR staffing coincided with higher turnover, but the benefit of more HR staff diminished past a point. The author noted more research was needed to establish cause and effect.

A June 2024 ADP SPARK article added detail: organizations with less than 0.5 HR staff per 100 employees had 5.8 percent monthly turnover, while those with 2.5 to 3.5 HR staff per 100 employees saw monthly turnover of 4.5 percent.

How should you read these numbers?

Benchmarks are averages across very different employers. Before you compare, check three things:

  1. Who counts as HR. Do you include payroll, recruiting, benefits, learning and HRIS staff? ADP's data comes from payroll job classifications, which may differ from your org chart.
  2. What is outsourced. A company using a PEO or outsourced recruiting will look lean on paper.
  3. Correlation versus causation. Companies with well-staffed HR may also invest more in pay and management, which affects turnover too.

Factors that push your HR staffing up or down

FactorPushes ratio upPushes ratio down
Workforce typeHigh-turnover frontline, hourly, shift-basedStable salaried professionals
LocationsMany sites, many states or countriesSingle location
Compliance loadUnions, regulated industries, multi-state payrollSimple, single-jurisdiction rules
Hiring volumeRapid growth or seasonal hiringLow hiring needs
TechnologyManual processes, disconnected systemsIntegrated HRIS, self-service, automation
Manager capabilityManagers escalate everything to HRTrained managers handle routine issues

A practical way to size your HR team

  1. Calculate your current ratio using a clear definition of HR roles, including contractors.
  2. Map workload by activity: recruiting, employee relations, payroll, benefits, compliance, systems and strategic projects. Estimate hours per week for each.
  3. Track signals of strain: time to fill, case backlog, payroll error rates, overtime among HR staff and turnover. Our guide to tracking HR KPIs in your HRMS covers how to set those up.
  4. Compare against benchmarks for your size and industry, treating them as a sanity check.
  5. Decide between headcount and leverage. Sometimes self-service, better integrations or manager training remove more work than a new hire would.

Understaffing has human costs inside HR as well; our piece on HR burnout looks at the emotional load. Overstaffing creates a different risk: HR roles that cannot show impact are among the first examined in cutbacks, as discussed in which HR functions are most vulnerable to layoffs.

Frequently Asked Questions

What is a good HR-to-employee ratio?

There is no universal figure. ADP data puts the average around 2.6 HR staff per 100 employees, with smaller firms often higher. The right ratio for you depends on workforce type, locations, compliance complexity, hiring volume and how much HR work is automated or outsourced. Use benchmarks as a reference, then validate against workload.

Does more HR staff reduce employee turnover?

ADP Research found lower HR staffing coincided with higher turnover, and the lowest-staffed group had higher monthly turnover than better-staffed organizations. However, the benefit diminished past a certain level, and ADP noted causation was not established. Other factors such as pay, scheduling and management quality also drive turnover.

Why do small companies have higher HR ratios?

Some HR work is fixed regardless of headcount: payroll setup, benefits administration, compliance filings and policy maintenance. A company with 40 employees still needs those tasks done, so even one HR person produces a high ratio. As companies grow, that fixed work spreads across more employees and the ratio tends to fall.

Next steps

Calculate your current ratio with a clear definition, gather six months of workload and strain metrics, and compare both to ADP's reference points. Then build a short business case that names specific work to be added, automated or moved to managers before requesting headcount.

Last reviewed: October 2026.

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