Gmax is the most widely referenced safety metric in synthetic turf – and one of the most misunderstood. It appears in field specifications, certification requirements, and procurement documents across the industry, yet few field owners or specifiers can explain what it actually measures, why it matters, or why a field that passes at installation may not pass two years later.

This article explains g-max in plain technical terms: what it measures, how it is tested, what thresholds apply across different field standards, and what drives g-max values up over a field’s lifecycle. Understanding g-max is the first step toward specifying, procuring, and maintaining a synthetic turf field that performs safely throughout its service life — not just on installation day.

What g-max Measures

g-max measures the peak deceleration force transmitted to an object, in athletic surface testing, a standardized missile head, during a controlled impact onto the surface. It is expressed as a multiple of gravitational acceleration (g). A g-max of 100g means the surface transmitted a peak deceleration force 100 times greater than gravitational acceleration during the impact event.

Lower g-max values indicate better impact attenuation, the surface absorbed more energy before transmitting it upward. Higher g-max values indicate a harder surface that transmits more force to the athlete upon contact.

How g-max is Tested

g-max is measured using a standardized drop test protocol defined by ASTM F355 and EN 1177. A missile of defined mass and geometry is dropped from a specified height onto the surface. Accelerometers embedded in the missile record the deceleration profile throughout the impact event. The peak value of that deceleration curve is g-max.

Testing is performed by ISO 17025-accredited independent laboratories. Act Global uses Firefly Sports Testing, Labosport, and Sports Labs — the same laboratories that test Super Bowl fields and FIFA World Cup venues. Results from internal or manufacturer-conducted testing are not considered independently verified.

g-max Thresholds by Standard

Different governing bodies and standards organizations define acceptable g-max ranges for their specific applications. The following thresholds represent the most commonly referenced benchmarks in North American and international synthetic turf specification:

ASTM F1936 – General Athletic Surfaces

Maximum g-max: 200g
This is the baseline threshold for athletic surfaces in the United States. A surface exceeding 200g is considered unsafe for athletic use under ASTM standards.

FIFA Quality Program

g-max range: 60–180g
FIFA’s Quality Program establishes both a minimum and maximum g-max threshold. A surface below 60g is considered too soft, it may absorb energy in ways that affect ball behavior and athlete biomechanics. A surface above 180g approaches unsafe hardness levels.

NFL Field Standards

The NFL does not publish a single universal g-max threshold. Instead, NFL fields are subject to independent testing at installation and ongoing monitoring throughout the season. Field performance data is tracked by the NFL and NFLPA as part of the league’s field safety initiative.

World Rugby

g-max range: 35–200g for synthetic turf
World Rugby’s thresholds are broader than FIFA’s, reflecting the different biomechanical demands of rugby vs. football.

Why g-max Changes Over Time

g-max at installation is not g-max at year three. This is the most operationally critical fact about this metric, and the one most commonly overlooked in procurement and maintenance planning.

Several mechanisms drive g-max upward over a field’s service life:

Infill Compaction

As infill particles, crumb rubber, sand, cork, or organic alternatives, experience repeated loading from athletic activity, they compact. Compacted infill has less capacity to absorb impact energy, which transmits more force to the athlete and increases g-max. High-traffic zones compact significantly faster than low-traffic areas, creating localized zones of elevated Gmax even when the overall field average remains within threshold.

Fiber Flattening

Synthetic turf fibers experience progressive flattening under repeated use and UV exposure. Flattened fibers contribute less to impact energy absorption, effectively reducing the cushioning contribution of the fiber layer and increasing the load on infill and shock pad.

Base Settlement

Base materials, crushed stone, recycled asphalt, or engineered base systems, can settle unevenly over time, particularly in areas subject to heavy vehicle traffic or poor drainage. Base settlement affects surface stiffness and can elevate g-max in localized areas independent of fiber or infill condition.

Gmax and Lifecycle Management

A field that passes g-max thresholds at installation requires active lifecycle management to maintain those results. Industry best practice includes:

Annual independent g-max testing by an ISO 17025-accredited laboratory
Zone-by-zone measurement, not just a single field average, to identify localized high-Gmax areas
Infill decompaction and redistribution as part of a structured maintenance program
Shock pad inspection at the time of fiber replacement to assess whether pad performance has degraded

Fields without a structured maintenance and retesting program cannot reliably claim ongoing safety compliance regardless of their installation test results.

Act Global Perspective

Act Global specifies g-max as a system-level design target, not a post-installation compliance checkbox. Every Act Global sports turf system is engineered with fiber density, infill type, infill depth, shock pad specification, and base design selected in combination to achieve and maintain target g-max values throughout the field’s service life, not just at installation.

Published g-max test results for Act Global systems are conducted exclusively by ISO 17025-accredited independent laboratories, Firefly Sports Testing, Labosport, and Sports Labs. These results are available in Act Global’s Test Report Center.

Act Global systems have been independently tested and installed at NFL venues and in 90+ countries across climates and use intensities. The consistency of g-max results across those installations reflects system-level engineering, not single-component specification.

Frequently Asked Questions

What is a good Gmax value for a synthetic turf field?

For most synthetic turf applications, a g-maxbetween 80–150g represents a well-performing surface, firm enough for predictable athletic movement, soft enough to attenuate impact effectively. FIFA Quality standards require 60–180g. ASTM F1936 sets the absolute maximum at 200g. Fields consistently testing below 80g may be over-cushioned, which can affect ball behavior and traction consistency.

How often should g-max be tested?

Industry best practice is annual independent g-max testing by an ISO 17025-accredited laboratory. High-use fields, those exceeding 1,000 hours of use per year should consider biannual testing. Zone-by-zone measurement is strongly recommended over single-point or averaged field results, as high-traffic areas compact significantly faster than low-use zones.

Can g-max be improved on an existing field without full replacement?

Yes, in many cases. If elevated g-max is caused by infill compaction, professional infill decompaction and redistribution can restore g-max values to acceptable ranges. If the shock pad has degraded or the fiber is severely flattened, more extensive remediation may be required. An independent assessment by an accredited laboratory is the correct first step before any remediation work.

Does a higher shock pad thickness always mean lower g-max?

Not necessarily. Shock pad performance depends on material type, density, and thickness, not thickness alone. A thin, high-performance shock pad can outperform a thick, low-density pad on g-max attenuation. Shock pad specification should be based on system-level testing data, not pad thickness as a standalone specification criterion.

Is Gmax the same as HIC?

No. g-max measures peak deceleration force — the highest point on the impact curve. HIC (Head Injury Criterion) is calculated from the full shape of that curve over time and is considered a more comprehensive indicator of traumatic brain injury risk. Both metrics are measured in the same drop test. A surface can have an acceptable g-max and still produce a concerning HIC value depending on the shape of the deceleration curve.

Related Resources

What Makes Synthetic Turf Safe? A Science-Based Definition → (coming soon)
HIC Explained — Head Injury Criterion for Field Owners (coming soon)
Rotational Resistance & Traction — Lower-Extremity Injury Risk (coming soon)
Act Global Test Report Center

The content in this article reflects Act Global’s interpretation of publicly available independent test data, ASTM standards, FIFA Quality Program documentation, and peer-reviewed research on synthetic turf surface performance. It is provided for educational purposes only and does not constitute medical, legal, or engineering advice. Gmax thresholds cited reflect published standards as of the date of this article — refer to the relevant governing body for current certification requirements. Refer to original sources and accredited testing laboratories for complete methodology and findings.