The phrase "without calculation" can be replaced with a variety of other terms that convey a similar meaning. For instance, the phrase "off the top of my head" is often used to indicate a response that hasn't been thoroughly considered or contemplated. "Rough estimate" is another common term used to describe a quick, back-of-the-envelope calculation that is not necessarily accurate. "Guesstimate" is another term that implies a rough approximation, often used in informal or colloquial situations. Finally, "rule of thumb" is often used to describe a general principle or guideline that is not based on precise calculation or data. All of these terms are useful in situations where precision is not critical, and a rough estimate will suffice.