Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Shared/Drawing.php
public static function pixelsToCellDimension($pValue, \PhpOffice\PhpSpreadsheet\Style\Font $pDefaultFont)
    {
        // Font name and size
        $name = $pDefaultFont->getName();
        $size = $pDefaultFont->getSize();

        if (isset(Font::$defaultColumnWidths[$name][$size])) {
            // Exact width can be determined
            $colWidth = $pValue * Font::$defaultColumnWidths[$name][$size]['width'] / Font::$defaultColumnWidths[$name][$size]['px'];
        } else {
            // We don't have data for this particular font and size, use approximation by
            // extrapolating from Calibri 11
            $colWidth = $pValue * 11 * Font::$defaultColumnWidths['Calibri'][11]['width'] / Font::$defaultColumnWidths['Calibri'][11]['px'] / $size;
        }

        return $colWidth;
    }
public static function pixelsToCellDimension($pValue, \PhpOffice\PhpSpreadsheet\Style\Font $pDefaultFont)
    {
        // Font name and size
        $name = $pDefaultFont->getName();
        $size = $pDefaultFont->getSize();

        if (isset(Font::$defaultColumnWidths[$name][$size])) {
            // Exact width can be determined
            $colWidth = $pValue * Font::$defaultColumnWidths[$name][$size]['width'] / Font::$defaultColumnWidths[$name][$size]['px'];
        } else {
            // We don't have data for this particular font and size, use approximation by
            // extrapolating from Calibri 11
            $colWidth = $pValue * 11 * Font::$defaultColumnWidths['Calibri'][11]['width'] / Font::$defaultColumnWidths['Calibri'][11]['px'] / $size;
        }

        return $colWidth;
    }
Convert pixels to column width. Exact algorithm not known.
By inspection of a real Excel file using Calibri 11, one finds 1000px ~ 142.85546875
This gives a conversion factor of 7. Also, we assume that pixels and font size are proportional.

@param int $pValue Value in pixels
@param \PhpOffice\PhpSpreadsheet\Style\Font $pDefaultFont Default font of the workbook

@return int Value in cell dimension