how to put log in a calculator

Quick answer: how to put log in a calculator

On most scientific calculators, you can compute logarithms using the LOG button (base 10) or LN button (base e). To find a log with a different base, use the change-of-base formula:

So if you need log base 2 of 50, type:

What “log” means on a calculator

A logarithm answers this question: “What exponent gives me this number?”

• log₁₀(100) = 2, because 10² = 100
• ln(e³) = 3, because e³ = e³
• log₂(8) = 3, because 2³ = 8

That’s why logs and exponents are inverse operations.

Step-by-step: entering log on a scientific calculator

1) For common log (base 10)

• Press LOG
• Type the number
• Close parenthesis if needed
• Press =

Example: log(1000) = 3.

2) For natural log (base e)

• Press LN
• Type the number
• Press =

Example: ln(7.389...) ≈ 2.

3) For log with another base

If your calculator doesn’t have a dedicated logBASE key, use:

or

Both are correct, as long as you use the same log type in numerator and denominator.

How to type logs on phones and computers

On phone calculator apps

Switch to scientific mode (rotate phone sideways or open advanced mode). Look for log and ln.

On Google search

• Type log(250) for base 10
• Type ln(250) for natural log
• Type log(250)/log(3) for base-3 log

On spreadsheets

• Excel/Google Sheets: =LOG(number, base)
• Natural log: =LN(number)

Common mistakes (and how to avoid them)

• Using log on zero or negative values: logarithm inputs must be greater than 0.
• Mixing base types: don’t divide log(x) by ln(b); use matching functions.
• Forgetting parentheses: type full expressions clearly, especially in long equations.
• Confusing log and antilog: log finds the exponent; antilog raises base to an exponent.

Worked examples

Example 1: log₁₀(500)

Press LOG, type 500, then equals. Result: 2.69897...

Example 2: ln(20)

Press LN, type 20, then equals. Result: 2.9957...

Example 3: log₂(40)

Use change of base:

Final tip

If you’re learning algebra, chemistry, statistics, or finance, logs show up constantly. Focus on three habits:

• Know which base you need
• Check that the input is positive
• Use change-of-base when your calculator has only LOG and LN

Use the calculator at the top of this page to practice quickly and verify your manual keystrokes.