Calculate FF (Floor Flatness) and FL (Floor Levelness) F-numbers per ACI 117 from your elevation grid. This is the only free online calculator for ACI 117 F-numbers — essential for warehouse slabs, data center floors, and any high-tolerance concrete flatwork. Enter your shot grid, set your spec requirements, and get instant pass/fail results with problem areas highlighted.
The F-number system, standardized in ACI 117, uses two metrics to describe concrete floor quality: FF (Floor Flatness) and FL (Floor Levelness). Both are dimensionless numbers where higher is better. FF 25 is the conventional minimum; superflat floors for narrow-aisle warehouses can require FF 100+.
FF measures local flatness — bumps and dips within a 10-foot area. It's sensitive to screed marks, aggregate pop-outs, and trowel marks. FL measures global levelness — how much the floor tilts over longer distances. A floor can have excellent FF (very smooth locally) but poor FL (one end lower than the other).
For turret truck operations (VNAHE — Very Narrow Aisle High Equipment), both FF and FL matter critically. A poor FL causes vehicles to tilt, reducing load capacity and safety. Most manufacturers specify FF/FL requirements in their service agreements.
| Floor Class | Min FF | Min FL | Typical Use |
|---|---|---|---|
| Conventional | 20 | 15 | Residential, light commercial |
| Standard | 25 | 20 | General commercial, retail |
| Industrial | 35 | 25 | Heavy manufacturing, general warehouse |
| High-tolerance | 50 | 35 | Distribution centers, food processing |
| Moderately flat | 50 | 35 | Reach truck operations |
| Superflat | 60+ | 40+ | VNA/VNAHE turret trucks |
| Superflat+ | 100+ | 50+ | Data centers, high-precision manufacturing |
F-numbers are a system for measuring and specifying concrete floor flatness and levelness per ACI 117. FF (Floor Flatness) measures local bumps and dips over short distances. FL (Floor Levelness) measures how level the floor is over longer distances. Higher numbers mean flatter/more level floors.
Conventional warehouses typically require FF 25 / FL 20 minimum. High-traffic rack-supported buildings often spec FF 35 / FL 25. Narrow-aisle turret truck operations ("superflat") require FF 50–100 / FL 35–50 or higher. Data centers often require FF 50+ for raised floor systems.
FF is calculated from "q values" — differential elevations between adjacent measurement points 12 inches apart along measurement lines. FF = 4.57 / √(mean of q²). A lower mean differential means a higher (better) FF number.
FL uses "d values" — second differences (differentials of differentials) that capture waviness over 10-foot intervals. FL = 3.04 / √(mean of d²). The 10-foot baseline detects longer-wavelength floor undulations that affect vehicle stability.
ACI 117 requires F-number measurements within 72 hours of concrete placement, before any curing compound affects the surface. Measurements must be taken using a Dipstick floor profiler or equivalent instrument along random sample lines perpendicular to the placement direction.
A superflat floor is typically defined as FF 50 / FL 30 or higher. These floors are required for very narrow aisle (VNA) warehouses, turret truck operations, and data center raised floors. They require specialized concrete placement, laser screeding, and a floor flatness contractor.
Calculate ACI 117 Floor Flatness (FF) and Floor Levelness (FL) F-numbers from elevation measurements. Used by concrete contractors, flooring inspectors, and QC engineers on warehouse, data center, and industrial slab projects.
Get a Dipstick floor profiler or laser level for ACI 117 F-number measurements.
Shop Express Tools →F-numbers are a system for measuring and specifying concrete floor flatness and levelness per ACI 117. FF (Floor Flatness) measures local bumps and dips over short distances. FL (Floor Levelness) measures how level the floor is over longer distances. Higher numbers mean flatter/more level floors.
Conventional warehouses typically require FF 25 / FL 20 minimum. High-traffic rack-supported buildings often spec FF 35 / FL 25. Narrow-aisle turret truck operations ("superflat") require FF 50–100 / FL 35–50 or higher. Data centers often require FF 50+ for raised floor systems.
FF is calculated from "q values" — differential elevations between adjacent measurement points 12 inches apart along measurement lines. FF = 4.57 / √(mean of q²). A lower mean differential means a higher (better) FF number.
FL uses "d values" — second differences (differentials of differentials) that capture waviness over 10-foot intervals. FL = 3.04 / √(mean of d²). The 10-foot baseline detects longer-wavelength floor undulations that affect vehicle stability.
ACI 117 requires F-number measurements within 72 hours of concrete placement, before any curing compound affects the surface. Measurements must be taken using a Dipstick floor profiler or equivalent instrument along random sample lines perpendicular to the placement direction.
A superflat floor is typically defined as FF 50 / FL 30 or higher. These floors are required for very narrow aisle (VNA) warehouses, turret truck operations, and data center raised floors. They require specialized concrete placement, laser screeding, and a floor flatness contractor.
Tip: Fill cells left-to-right, row by row. Red cells = out-of-spec areas.