Technical Reference
G-Max testing for synthetic turf.
What G-max actually measures, how the ASTM F355 and F1936 tests run in the field, what numbers to target at each tier of use, and why a field that passed at install can fail three years later.
G-max is the single number that decides whether a synthetic turf field is safe to play on. It shows up in every serious bid spec, every warranty, and every post-injury liability review. This page explains what the number means, which ASTM standards govern it, what targets we build to, and how testing actually happens on the ground. It is written for athletic directors, facilities managers, and architects reviewing or writing a field specification.
What G-max measures
G-max is the peak deceleration a mass experiences at the moment it strikes a surface, expressed in gravities (g). Drop a weight on concrete and it stops almost instantly: very high deceleration, very high G-max. Drop the same weight on a surface that gives, and the stop is spread over more time and distance: lower deceleration, lower G-max. That give is what the industry calls shock attenuation. In practical terms, G-max is a proxy for what a player’s head and body experience when they hit the field.
Lower is more forgiving, but not without limit. A surface that is too soft compromises footing and ball response. The spec ranges below exist because the industry has converged on a band that is safe on impact and still plays like a field.
ASTM F355: the test method
ASTM F355 defines how the measurement is taken. Procedure A, the one used for turf fields, drops a flat-faced cylindrical missile weighing about 20 pounds from a height of 24 inches onto the surface. Accelerometers inside the missile record peak deceleration during impact. F355 is a test method, not a pass/fail specification: it tells you how to get the number, not what the number has to be.
ASTM F1936: the field standard
ASTM F1936 is the specification that applies F355 testing to synthetic turf athletic fields, and it is where the pass/fail line lives: no test point on the field may exceed 200 g-max. That 200 ceiling is the most widely recognized safety threshold in the industry, and it is the number referenced when a field is described as failing. F1936 also defines where and how the field is tested, which matters more than most specs acknowledge, because a field average can look fine while one compacted high-traffic zone fails.
Target ranges by surface tier
200 is the failure line, not the target. Real specs aim much lower:
- G-max 100 to 120: professional and elite competitive fields. The most forgiving band that still plays fast.
- G-max 120 to 160: the band most school, park, and recreational specs land in. Many institutional specs are written as a maximum of 130 at installation.
- G-max 165: commonly specified as the end-of-warranty maximum for competitive fields. A field drifting past this is on notice.
- G-max above 200: fails ASTM F1936. The surface should come out of service until corrected.
Playgrounds are a different world: they are tested under ASTM F1292, which uses a headform and adds the Head Injury Criterion. Do not carry sports field targets over to playground surfacing or vice versa.
How a test day actually runs
A third-party technician lays out 10 test points distributed across the field per F1936, deliberately including high-wear areas: between the hash marks, goal mouths, the center of the field. At each point the missile is dropped three times. The first drop is discarded because it seats the infill; the second and third drops are averaged to produce that point’s reported g-max. Every point has to pass individually. The whole process takes a few hours and produces a report your facility should keep on file permanently.
How often to retest
ASTM does not set a retest calendar, so the spec has to. The cadence we recommend, and the one most school district and municipal specs use: baseline at installation, retest at the one-year mark, then annually for the life of the field. Retest sooner after heavy tournament use, visible infill migration in high-traffic zones, or a winter with repeated freeze-thaw cycles. Annual documentation is also what keeps a performance warranty enforceable: without a test history, a dispute over a year-8 failure becomes your word against the manufacturer’s.
What makes G-max drift
- Infill compaction: the number one cause. Foot traffic packs the infill dense and hard, and g-max climbs. Regular grooming and decompaction slows it.
- Infill migration: infill walks out of high-use zones. Less cushion depth means higher g-max exactly where players hit the ground most.
- Base problems: a poorly compacted or settling base changes the system stiffness underneath the turf. No amount of grooming fixes a base issue.
- Temperature and moisture: cold, dry conditions test harder than warm, damp ones. A borderline field can pass in September and fail in January, which is why specs should name test conditions.
How we build to hit the target
We do not chase G-max after the fact; we design for it. That means a base built to spec with documented compaction, a shock pad when the system needs one (always on concrete sub-floors and indoor installs, which contribute zero natural attenuation), and infill type and depth matched to the manufacturer’s tested system, not substituted on price. Every commercial field proposal we submit names the G-max target at install and at warranty end-of-life, and we document the base and pad work with drone photography before the turf goes down. For the full picture of the standards behind a bid spec, see our ASTM standards guide.
Spec Desk
Writing a bid spec? Start from our model spec document, or send us your RFP and we will respond within one business day.
G-Max testing FAQ
What ASTM standard covers G-max for turf?
Two standards work together. ASTM F355 is the test method: it defines the missile, the drop height, and how peak deceleration is recorded. ASTM F1936 is the field specification: it applies the F355 Procedure A test to synthetic turf athletic fields and sets the pass/fail ceiling of 200 g-max at every test point. Playgrounds use a different standard, ASTM F1292, which adds the Head Injury Criterion (HIC) calculation.
What is G-max shock attenuation?
G-max is the peak deceleration a falling mass experiences when it hits a surface, expressed in multiples of gravity (g). A lower G-max means the surface absorbs more of the impact and the body absorbs less. Shock attenuation is the general term for that energy-absorbing behavior. A concrete slab tests in the hundreds; a well-built synthetic turf field commonly tests between 120 and 160.
Is 160 a passing G-max level for a synthetic turf field?
Yes. The ASTM F1936 ceiling is 200 g-max, so 160 passes the standard. Whether it passes your spec is a separate question: many school district and municipal specs require 130 or lower at installation and 165 or lower for the life of the warranty. A field testing at 160 when new has little headroom for compaction, so we would look at the base and infill design before accepting it.
How often should G-max testing be done on a turf field?
ASTM does not mandate a retest interval, but the common institutional spec is: a baseline test at installation, a test at the one-year mark, and annual testing thereafter, all documented by a third party. Fields with heavy multi-sport use, visible infill migration, or a hard freeze-thaw winter should be tested more often. Keep every report on file for insurance and warranty purposes.
How does a G-max test day actually work?
A technician tests 10 points distributed across the field per ASTM F1936, including high-wear zones like the hash marks and goal areas. At each point the F355 missile is dropped three times from 24 inches. The first drop is discarded because it seats the infill, and the second and third drops are averaged to produce the reported g-max for that point. Every point must come in at or below the specified maximum.
What happens if a field tests above 200 g-max?
It fails ASTM F1936 and most industry guidance says it should come out of service until it is corrected. Common fixes, in order of cost: decompacting and grooming the infill, topping up migrated infill to the specified depth, and in worst cases rebuilding the base or adding a shock pad under new turf. A failing number is almost never the turf fiber itself; it is the infill and the base underneath.
Do playgrounds use the same G-max test as sports fields?
No. Playgrounds are governed by ASTM F1292, which drops an instrumented headform rather than the F355 flat missile and adds the HIC (Head Injury Criterion) calculation alongside g-max. The pass criteria are g-max at or below 200 and HIC at or below 1,000 at the rated critical fall height. A sports field G-max report does not certify a playground surface, and vice versa.
Can G-max be lowered without replacing the turf?
Often, yes. If the number is drifting up from compaction, mechanical decompaction and grooming of the infill can recover a meaningful amount. If infill has migrated out of high-wear zones, topping it back up to the specified depth helps. If the base itself is the problem, or the field was built without a shock pad and cannot hit spec, the fix runs deeper. We start with an infill depth survey before recommending anything structural.