Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Shared/Font.php
public static function getDefaultColumnWidthByFont(\PhpOffice\PhpSpreadsheet\Style\Font $font, $pPixels = false)
    {
        if (isset(self::$defaultColumnWidths[$font->getName()][$font->getSize()])) {
            // Exact width can be determined
            $columnWidth = $pPixels ?
                self::$defaultColumnWidths[$font->getName()][$font->getSize()]['px']
                    : self::$defaultColumnWidths[$font->getName()][$font->getSize()]['width'];
        } else {
            // We don't have data for this particular font and size, use approximation by
            // extrapolating from Calibri 11
            $columnWidth = $pPixels ?
                self::$defaultColumnWidths['Calibri'][11]['px']
                    : self::$defaultColumnWidths['Calibri'][11]['width'];
            $columnWidth = $columnWidth * $font->getSize() / 11;

            // Round pixels to closest integer
            if ($pPixels) {
                $columnWidth = (int) round($columnWidth);
            }
        }

        return $columnWidth;
    }
public static function getDefaultColumnWidthByFont(\PhpOffice\PhpSpreadsheet\Style\Font $font, $pPixels = false)
    {
        if (isset(self::$defaultColumnWidths[$font->getName()][$font->getSize()])) {
            // Exact width can be determined
            $columnWidth = $pPixels ?
                self::$defaultColumnWidths[$font->getName()][$font->getSize()]['px']
                    : self::$defaultColumnWidths[$font->getName()][$font->getSize()]['width'];
        } else {
            // We don't have data for this particular font and size, use approximation by
            // extrapolating from Calibri 11
            $columnWidth = $pPixels ?
                self::$defaultColumnWidths['Calibri'][11]['px']
                    : self::$defaultColumnWidths['Calibri'][11]['width'];
            $columnWidth = $columnWidth * $font->getSize() / 11;

            // Round pixels to closest integer
            if ($pPixels) {
                $columnWidth = (int) round($columnWidth);
            }
        }

        return $columnWidth;
    }
Get the effective column width for columns without a column dimension or column with width -1
For example, for Calibri 11 this is 9.140625 (64 px).

@param \PhpOffice\PhpSpreadsheet\Style\Font $font The workbooks default font
@param bool $pPixels true = return column width in pixels, false = return in OOXML units

@return mixed Column width