FF/FL Testing
Fmin Testing
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FF/FL Testing

  • FF/FL Testing
  • The F-Number System (authored by Allen Face) is the world’s foremost method for the specification and control of concrete floor flatness and levelness. The FF and FL Numbers apply to Random Traffic Floors.

  • For Flooring Contractors

    • for quick day-to-day floor profile quality control
    • to ensure compliance
    • for effective floor profile management

  • For Floor Owners and Specifiers

    • to define floor profile requirements explicitly
    • to ensure the required quality has been delivered


Profile quality is among the most important characteristics of any concrete floor. Furthermore, overt control of this feature during construction can lead indirectly to significant improvements in all other properties.

FF/FL Numbers replace all forms of the old ‘gap–under–the-straightedge’ type specification that have proven themselves to be unreliable, unmeasurable, and highly manipulatable. FF/FL Numbers have been formalized in ASTM since 1987 (ASTM E 1155M Standard Test Method for Determining FF Floor Flatness and FL Floor Levelness Numbers) and in ACI since 1989 (ACI 117 ).

Find out more about FF/FL testing! Click to start!
Make the individual concrete placements
Mark the measurement lines on the floor’s surface
Test the floor along the lines for FF and FL as set forth in ASTM E 1155M
Check the flatness (FF) and levelness (FL) on the profiling instrument’s screen
Download the collected data into Excel by a single click

Problems with All Gap-Under-the-Straightedge Type Tolerances

Floor profile finish quality has traditionally been specified by limiting the size of the gap to be measured under a freestanding straightedge (viz. DIN 18202). Thirty years ago, however, the technology for measuring floor profiles was forced to change in response to the ever more demanding needs of industrial warehouse operators. By the early 1990s, straightedge specifications had become obsolete. FF/FL Numbers provided an essential alternative to the recognized inadequacies of the straightedge method.

The straightedge procedure for judging floor irregularities has a number of serious liabilities:

  • Inability to test large areas(the test method is much too slow to use on a day-to-day basis)
  • Inability to conduct the test in a statistically legitimate manner
  • Inability to reproduce results
  • Susceptibility to manipulation

While many forms of the straightedge specification continue to be specified, they are rarely (if ever) tested and universally problematic.

FF/FL Floor Profile Tolerances

The FF/FL System provides the specifier, contractor, and owner with a convenient and precise method for communicating the profile requirements, for testing the results, and for equitably resolving any out-of-compliance work.

FF/FL Numbers provide statistical control over two distinct profile variables:

The 30 cm incremental curvature q measures the local flatness (FF)
The 3 m elevation difference z measures the local levelness (FL)

FF/FL Facts

  • Mathematically rigorous, realistic, repeatable, and uncorruptable
  • Infinitely adjustable; not limited to a few fixed categories; permits the accurate comparison of the flatness/levelness of any two floors
  • Grounded in elementary statistical control theory
  • Robust system leads to coherent, logical market behavior
  • Employs simple, convenient, easy-to-learn terminology
  • Proven through decades of successful use
  • Directly applicable to the control of hard-axle lift truck motions
  • Provides owners the floors they need at reasonable, competitive prices
  • Affords contractors full protection against the risks created by the present defective tolerances
  • Gives architects and engineers the reliable feedback they need to design and specify profile tolerances that are appropriate to the intended floor use
  • Relegates all the intimidating mathematics to the computer
  • Only requires specifiers to know the numbers that will make their clients happy
  • Only requires contractors to know how to build the specified numbers.

FF/FL Measurement

The FF/FL System’s advantages can best be realized through use of our state-of-the-art floor profilers (D-Meter® & F-Meter®). Any owner, contractor, or test lab can use this equipment to obtain instant feedback on the floor’s profile quality. These instruments not only calculate and display the floor’s FF/FL numbers on the spot, but also download all results into Excel with a single mouse click.

Contractor’s and Specifier’s Guide to the F-Numbers

The documents in our 'download' section provide a more detailed explanation of the FF/FL and Fmin systems and will help you incorporate these two powerful systems into your floor projects both quickly and easily.

FF qmax, mm FL z, mm Intended use
Conventional 25 4.6 15 20 conventional, non-special construction
Moderatly Flat 35 3.3 20 15.7 foot traffic
Flat 40 2.9 25 12.6 conventional warehouse
Very flat 60 1.9 35 9 high-elevation, high-speed conventional warehouse
Super flat 80 1.4 50 6.3 TV studio, ice rink
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