EN 324 1: 1993
Woodbased Panels – Determination of thickness, width and length
Part 1 gives methods for measuring the thickness, width and length of woodbased panels. It applies to whole flat boards.
Thickness
 A micrometer or similar measuring instrument having flat, parallel measuring surfaces of 16mm (± 1) diameter and an operating force of 4N (± 1) and graduated to allow readings to 0.05mm. Measurements are taken at approximately 50mm from the panel edges at points in each corner and in the middle of each side – 8 no. points in total per panel. Readings must be within 1% of the thickness but to be not less than 0.1mm. Average the 8 no. readings and express this figure to the nearest 0.1mm.
Length and width
 Measure both the length and width of each panel along two lines parallel to and at a distance of 100mm from the edges to an accuracy of 0.1% but not less than 1mm. Average the two readings each for length and width and express the results to the nearest 1mm.
In comparison – APA’s method for calculating the thickness, length and width:
Thickness
 Measure using a micrometer having anvils of diameter 19.1mm (+1.3mm/ – 0) or 3/4” (+ 0.05”/ 0) and an anvil pressure of not less than 34 kPa (5 psi) and not more than 69 kPa (10psi).
 Measure midwidth on one end of a panel. If the measurement is below minimum or above maximum requirements, then three additional measurements shall be taken – one at approximately midwidth on the opposite end and one at approximately midlength on each side of the panel.
 Calculate the average of these 4 readings. If the average lies between the minimum and maximum thickness for that specific performance category, then the panel is acceptable; if it is outside the minimum or maximum tolerance, then the panel is below/above thickness.
Performance Category thickness and tolerance for APA plywood panels
This is in line with US PS 119 Structural Plywood and US PS 218 Performance Rated OSB.
APA Plywood 
Performance Category 
Tolerance  

inches 
mm 

Sanded Unsanded 
≤3/4 >3/4 
±0.016 (1/64) ±3% 
±0.4 ±3% 
Touch sanded Overlaid 
≤13/16 >13/16 
±0.031 (1/32) ±5% 
±0.8 ±5%

Length and width
 A tolerance of + 0mm, – 1.6mm (1/16”) should be allowed on the specified length and width.