by Dr. Shipman, USDA

Relative values for cell size using various popular units of measure.

# cells/dm2 (2 sides) | # cells/inch | # cells/in2 (2 sides) | cell width in mm2 |

650 | 4.3 | 41.9 | 6.0 |

700 | 4.4 | 45.2 | 5.7 |

725 | 4.5 | 46.8 | 5.6 |

750 | 4.6 | 48.4 | 5.5 |

800 | 4.7 | 51.6 | 5.4 |

830 | 4.8 | 53.5 | 5.3 |

850 | 4.9 | 54.8 | 5.2 |

920 | 5.1 | 59.4 | 5.0 |

950 | 5.2 | 61.3 | 4.9 |

1050 | 5.4 | 67.7 | 4.7 |

Cells per square decimeter (dm2) is a useful unit of measure for understanding colony population dynamics and for developing management strategies, but, for practical field diagnostics it is easier to measure the width of a row of 10 cells measured side to side. A dm2 is an area 10 cm by 10 cm; cells on both sides of the comb area are counted. To convert cells per dm2 to cells per linear dm and then to mm per cell use equation 1:

**Equation 1:**

cells/dm2 = 2.31XN2 (where N is the number of cells per linear dm)

Example: 850 = 2.31 x (19.18)2

Divide 100 by cells per linear dm to obtain mm per cell

Example: 100 divided 19.2 = 5.2

To convert cells per in2 to inches per cell:

**Equation 2:**

cells/in2 = 2.31XN2 (where N = number of cells per inch)

Example: 54.8 = 2.31 x (4.87)2

**Equation 3:**

cells/dm2 = 15.5 X cells/in2

Example: 850 = 15.5 x 54.8

*The values in this column represent the width of a single cell as measured between centers of opposing cell walls. The actual cell interior width is one cell wall thickness less than this value.*