code/Debug/Helper/Data.php
public function formatMemorySize($size, $precision = 2)
    {
        $sizes = array(" Bytes", " KB", " MB", " GB", " TB", " PB", " EB", " ZB", " YB");
        if ($size == 0) {
            return $this->__('n/a');
        } else {
            $value = round($size / pow(1000, ($i = floor(log($size, 1000)))), $precision);
            $unitIndex = (int)$i;
            return $this->__('%s%s', $this->formatNumber($value, $precision), $sizes[$unitIndex]);
        }
    }
public function formatMemorySize($size, $precision = 2)
    {
        $sizes = array(" Bytes", " KB", " MB", " GB", " TB", " PB", " EB", " ZB", " YB");
        if ($size == 0) {
            return $this->__('n/a');
        } else {
            $value = round($size / pow(1000, ($i = floor(log($size, 1000)))), $precision);
            $unitIndex = (int)$i;
            return $this->__('%s%s', $this->formatNumber($value, $precision), $sizes[$unitIndex]);
        }
    }
Returns readable file size

@param int $size size in bytes
@param int $precision
@return string