PI-009: Seed Potato Tuber Inspection
Appendix 11: Oversize and Undersize

This page is part of the Guidance Document Repository (GDR).

Looking for related documents?
Search for related documents in the Guidance Document Repository

Requirements:

All documentation for any quantity of graded seed potatoes, whether in containers or in bulk must specify the minimum and maximum size of the graded tubers in millimeters. Unless there is a written contract between the buyer and seller, the minimum acceptable size must not be less than 30 mm and not more than 70 mm for long type varieties, or 80 mm for round type varieties. The percentage of undersize and oversize specimens should be noted in the identified area on the Seed Potato Tuber Inspection Report and must be written on all Seed Potato Certification Tags and Record of Bulk Movement for Seed Potatoes for that shipment.

For contractual agreements between a grower and purchaser for a specific size of graded seed potatoes, the agreement must state the minimum and maximum size in millimeters for the graded tubers. The grower or purchaser must retain, and produce when requested by the CFIA, a copy of the agreement clearly stating the minimum and maximum size. The minimum and maximum size from the agreement must be written on all Seed Potato Certification Tags and Record of Bulk Movement for Seed Potatoes for that shipment.

Scoring:

Unlike all other scoreable tuber diseases, defects and conditions, the percentage of oversize and undersize tubers are calculated by weight. The oversized and undersized tubers from the sample are determined with a sizer with square openings as described below, and weighed. The percentage of oversized and undersized tubers is calculated based on the total weight of the total sample and the exact weight of the oversized and undersized tubers. 95% of all tubers by weight must be between the maximum and minimum sizes.

The measurement for minimum and maximum diameter shall be the greatest length of a potato taken at right angles to the longitudinal axis, disregarding the position of the stem. To determine oversized and undersize specimens, a calibrated sizer with square openings is required. The sizer is adjusted to the appropriate upper or lower size limit and the tuber is moved and attempted to be fitted through the sizer. Tubers are scored as oversize or undersized as appropriate.

The following table details the weight and size, varieties round and long, for various potatoes.

Table 1: Potato Size and Weight for reference only
Weight - ounces Weight - grams Size: round varieties (approximate) - inches Size: round varieties (approximate) - millimeters Size: long varieties (approximate) - inches Size: long varieties (approximate) - millimeters
1 1/2 42.5 1 5/8 42 1 1/2 39
2 56.7 1 3/4 46 1 5/8 42
2 1/2 70.9 2 50 1 3/4 46
3 85.0 2 1/8 54 1 7/8 48
4 113.4 2 3/8 60 2 1/16 52
5 141.7 2 5/8 66 2 1/8 55
6 170.1 2 3/4 70 2 1/4 58
7 198.4 2 7/8 73 2 3/8 61
8 226.8 3 75 2 1/2 63
9 255.1 3 1/8 79 2 5/8 66
10 283.5 3 1/4 82 2 11/16 68
11 311.8 3 3/8 83 2 3/4 70
12 340.2 3 1/2 86 2 13/16 71
Date modified: