Logarithm Calculator
Logarithm calculator — solve for base, argument, or result in log_b(x)=y. Free online log calculator with natural-log mode, visuals, practice and study plan.
One curve, every base: steep at first, flat later. Doubling the argument always adds the same step to the answer — that is why logs tame earthquakes, acidity, and data spanning orders of magnitude.
- Grade level
- 9–12 + College
- Curriculum band
- Difficulty
- Intermediate
- For this topic
- Time to master
- 2 weeks
- With daily practice
- Tools on page
- 12 on page
- Calculator + practice
Calculator
Log Values — fill any two
Logarithm Summary
Breakdown
| Property | Value |
|---|---|
| log₁₀(x) — common | 3 |
| ln(x) — natural | 6.907755278982 |
| log₂(x) — binary | 9.965784284662 |
| Check: b^y | 999.999999999999 |
Results
Result (y)
3
Solved from base and argument
10
Logarithm base
1000
The value inside the logarithm
3
Common logarithm of the argument
6.907755278982
Natural logarithm of the argument
9.965784284662
Binary logarithm of the argument
Results follow real-number logarithm rules for the inputs given. The base must be positive and not 1, and the argument must be positive.
Statistics
Live readouts from your current inputs — the curve, bars and cards all move together. Change any field to watch tens, doublings and natural growth stay in sync.
Answer y
3
log(10)(1000)
Doublings (log₂)
9.965784284662
Times ×2 to reach x
Tens (log₁₀)
3
Orders of magnitude
Check b^y
999.999999999999
Must equal x
Visualizations
log₁₀ vs ln vs log₂
Log curve sampling (base = 10)
Result scale
Logarithmic curve (base = 10) — fast start, slow finish
Formula
A logarithm is the exponent that turns the base into the argument. Change-of-base rewrites any log with natural logs; product, quotient, and power rules split and join log expressions.
Alternative Form
Variables
| Symbol | Name | Unit | Description |
|---|---|---|---|
| b | Base | number | Raised to y to get x; > 0, ≠ 1 |
| x | Argument | number | The value inside the log; > 0 |
| y | Result | number | The exponent answering the log |
| e | Euler's number | constant | ≈ 2.71828 for natural logs |
| ln | Natural log | number | log base e |
| log₁₀ | Common log | number | log base 10 |
| log₂ | Binary log | number | log base 2 |
Explanation
Logs compress multiplication into addition: each unit step on a log scale multiplies the underlying value by the base, which is why they tame earthquakes, acidity, loudness, and data spanning orders of magnitude.
Derivation
From x = b^y take logs: ln(x) = y·ln(b), so y = ln(x)/ln(b). Product: ln(xy) = ln(x)+ln(y) exponentiated. Power: ln(x^y) = y·ln(x). Base solve: b = x^(1/y).
Step-by-Step Calculation
Follow each step to understand how the result is calculated from your inputs.
Read the equation as "b to what power gives x?"
Apply the change-of-base formula with natural logs.
Verify by exponentiating back.
Read the companion logarithms of the same argument.
Confirm domain rules held.
State the final equality.
Worked Examples
See how the calculator works with different scenarios.
Scenario
Compute log₁₀(1000).
Inputs
Calculation
y = ln(1000)/ln(10) = 6.908/2.303 = 3
Result
3
Interpretation
Three tens multiply to a thousand — the exponent counts the zeros.
Understanding Your Result
Your Result: Result (y): 3
Typical range: log₁₀(1000) = 3; ln(e) = 1; log₂(1024) = 10; pH spans 0–14; decibels span whisper (~20) to jet (~140).
What This Means
The result is the exponent the base needs to produce the argument, with log₁₀, ln, and log₂ translations of the same argument alongside.
Why It Matters
Richter, pH, decibels, algorithm complexity, and compound growth all speak logarithm — solving log_b(x) = y is reading those dialects.
Professional Interpretation
Match the base to the domain: 10 for science scales, e for calculus and growth, 2 for computing.
Recommendations
- •Use e-mode for calculus and growth work
- •Reach for base 10 on Richter/pH/decibel scales
- •Reach for base 2 on complexity and bits
- •Convert forms to double-check: b^y must equal x
- •Guard domains: b > 0, b ≠ 1, x > 0
- •Combine terms with product/quotient rules first
Learn — The Complete Guide
A logarithm inverts exponentiation: log_b(x) is the power that turns b into x. This calculator solves any missing piece of log_b(x) = y.
The core concept
If x = b^y then y = log_b(x). Common log (10) counts tens, natural log (e) fits calculus, binary log (2) counts doublings — one idea, three favorite bases.
- A log is a question: “b to WHAT power gives x?”
- Each +1 in log-land means ×base in number-land
- Base 10 counts tens · base e fits calculus · base 2 counts doublings
- Logs turn multiplication into addition (and division into subtraction)
Derivations — why the formulas work
Change of base — from x = b^y
- 1x = b^y
- 2ln(x) = ln(b^y)
- 3ln(x) = y · ln(b)
- 4y = ln(x) / ln(b) ✓
Product rule — from exponent addition
- 1Let a = log_b(x), c = log_b(y)
- 2x = b^a, y = b^c
- 3xy = b^(a+c)
- 4log_b(xy) = a + c ✓
Solve for the base — from x = b^y
- 1x = b^y
- 2Raise both sides to 1/y: x^(1/y) = b
- 3b = x^(1/y) ✓
- 4Requires y ≠ 0, b > 0, b ≠ 1
Where you meet this in real life
Learn this first — prerequisites in order
- 1Exponents: evaluate b^y including negative and fractional powers
- 2Roots: undo powers (cube root inverts cubing, as in b = x^(1/y))
- 3Functions & inverses: read log as the inverse of exponential
- 4Scientific notation: feel orders of magnitude (10³ vs 10⁶)
Careers that use this daily
- •Chemist — pH, buffers, reaction kinetics
- •Audio / acoustics engineer — decibels, filters, room tuning
- •Software engineer — complexity, entropy, data scales
- •Geophysicist — magnitude and intensity scales
- •Finance quant — log returns and continuous compounding
Why it helps
- •Solves any one of base, argument, or result
- •Natural-log mode for calculus workflows
- •Instant log₁₀ / ln / log₂ reference trio
- •Log curve shows diminishing-returns shape
- •Domain violations explained, not silently wrong
Best practices
- •Verify with the inverse: compute b^y and compare
- •Combine log terms before solving equations
- •Check for extraneous roots (argument must stay positive)
- •Pick the base your field expects
- •Use change-of-base on limited calculators
Limitations — what this tool does not do
- •Real numbers only — no complex logs of negatives
- •Base must be positive and not 1
- •Argument must be strictly positive
- •Display rounds to 12 significant digits
Curriculum map — where this topic lives in school
| Level | Grades | Standards | Skills |
|---|---|---|---|
| Algebra II | 9–10 | HSF-LE, HSF-BF | Evaluate logs · Flip log/exp forms · Domain rules |
| Precalculus | 10–12 | HSF-LE, HSF-IF | Log rules · Log equations · Graph transformations |
| AP Calculus / STEM | 11–College | AP CALC, HSF-LE | ln and e · d/dx ln(x) = 1/x · Growth/decay models |
Timeline — how this idea grew up
1614
Napier publishes log tables
John Napier’s Mirifici Logarithmorum turns multiplication into addition — astronomers halve their arithmetic overnight.
1620s
Slide rules take over
Gunter’s scale and Oughtred’s sliding sticks put logs in every engineer’s pocket for 350 years.
1748
Euler crowns e
Euler’s Introductio ties natural logs to e, calculus, and continuous growth — ln becomes the mathematician’s home base.
1935– today
Logs go mainstream
Richter (1935), pH, decibels, bits and Big-O carry logs into news, labs and code — then calculators make tables obsolete.
A little history
- • John Napier published the first log tables in 1614 to spare astronomers heavy multiplication.
- • The word “logarithm” joins Greek logos (ratio) + arithmos (number).
- • Slide rules — physical logarithms — designed everything from steam engines to Apollo.
Exam-day checklist
- • Write the flip first: y = log_b(x) → x = b^y, then solve the power.
- • Combine to one log per side before exponentiating.
- • Check every candidate: base > 0, base ≠ 1, argument > 0.
- • Estimate with nearby powers (log₁₀ 500 ≈ 2.7, between 100 and 1000).
Myths vs facts
Practical Tips
- •Leave one field blank to auto-solve it
- •Tick e-mode for natural logarithms
- •Verify: raise the base to the answer
- •Estimate with powers of the base first
- •Use change-of-base on basic calculators
- •Watch parentheses in log(x^y) vs (log x)^y
- •Reject solutions with non-positive arguments
Common Mistakes
Assumptions
This calculator makes the following assumptions to provide estimates:
Limitations
Be aware of these limitations when using this calculator:
Frequently Asked Questions
Answers to common questions about this calculator.
What is a logarithm?
What is the logarithm of 1?
What is the logarithm of the base itself?
What is the logarithm of 0?
Can you take the logarithm of a negative number?
What is the common logarithm (base 10)?
What is the natural logarithm (base e)?
What is the binary logarithm (base 2)?
What is the difference between log and ln?
Which base should I choose?
What is the product rule for logarithms?
What is the quotient rule for logarithms?
What is the power rule for logarithms?
What is the change of base formula?
How do I convert between logarithmic and exponential form?
How do I solve for the result y in log_b(x) = y?
How do I solve for the argument x?
How do I solve for the base b?
What is antilog?
Why is base 1 not allowed?
Why must the base be positive?
What are extraneous roots in log equations?
What are the most common logarithm mistakes?
How does pH use logarithms?
How does the Richter scale use logarithms?
How do decibels use logarithms?
Where do logarithms appear in computing and finance?
How do I use this logarithm calculator?
How do I verify my logarithm answer?
Why does the calculator show log₁₀, ln, and log₂ together?
Related Calculators
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Related Guides
Deepen your understanding with these educational resources.
Glossary
Technical terms used in mortgage calculations explained in plain language.
- Logarithm
- The exponent y with b^y = x, written log_b(x).
- Base
- The b in log_b(x); must be > 0 and ≠ 1.
- Argument
- The x inside the logarithm; must be > 0.
- Natural log
- Log base e, written ln(x).
- Common log
- Log base 10, written log(x).
- Binary log
- Log base 2, written log₂(x).
- Antilog
- The inverse: antilog(y) = b^y.
- Change of base
- log_b(x) = log_k(x)/log_k(b) for any valid k.
- Log scale
- Equal spacing per equal ratio; tames wide ranges.
- Domain
- Valid inputs: b > 0, b ≠ 1, x > 0.
Authoritative References
Trusted sources and standards referenced by this calculator.
Applicable Standards
Diagrams & Illustrations
Visual intuition for every core idea. Select a card to enlarge it.
Did You Know?
Short intuition builders — great for class warm-ups.
Slide rules ran the world
Before pocket calculators, engineers multiplied with logs etched on sliding sticks — Apollo trajectories were flown on a Pickett slide rule.
Your ears are logarithmic
Perceived loudness follows Weber–Fechner: +10 dB sounds roughly twice as loud but carries 10× the power. Decibels are just log₁₀ in disguise.
log₂(1024) = 10 exactly
That coincidence (2¹⁰ ≈ 10³) is why 1 KB = 1024 bytes and why computer scientists think in binary logs.
pH is a flipped log
pH = −log₁₀[H⁺]: each single pH step means a tenfold change in acidity. Lemon juice (pH 2) is 10,000× more acidic than pure water (pH 7).
Compare Side by Side
Same argument, three favorite bases — computer science counts doublings, calculus uses e, science counts tens.
| Base | x = 1000 | Best for | log value |
|---|---|---|---|
| Base 2 (binary) | log₂(1000) | CS · bits · trees | 9.965784284662 |
| Base e (natural) | ln(1000) | Calculus · growth | 6.907755278982 |
| Base 10 (common) | log₁₀(1000) | Science · pH · dB | 3 |
Recent Calculations
Your last runs on this page — stored only in this browser, never uploaded.
log(10)(1000) = 3
Current inputs — live
Study Plan
A week-by-week path from prerequisites to mastery. Your checklist progress saves in this browser.
Prerequisites
- ▸Exponents and roots (b^y, fractional powers)
- ▸Function inverses (undoing an operation)
- ▸Scientific notation and orders of magnitude
Mastery progress — 0%
- I can flip between log and exponential form instantly
- I can solve for base, argument, or result
- I can apply all four log rules without notes
- I can explain why log(0) and log(negatives) fail
- I can pick the right base for a science/CS problem
- 1
Week 1 · ~20 min/day
Read logs as questions
Goals
- Translate y = log_b(x) ⟺ x = b^y both ways
- Evaluate log₁₀ and log₂ of powers mentally
- State the domain: b > 0, b ≠ 1, x > 0
Practice
Do 10 “powers first” reps: 10³ = 1000 → log₁₀(1000) = 3, 2⁵ = 32 → log₂(32) = 5.
- 2
Week 2 · ~25 min/day
Rules + equations
Goals
- Apply product, quotient, power and change-of-base rules
- Solve log_b(x) = y for each missing letter
- Reject extraneous roots with x ≤ 0
Practice
Solve 5 equations by combining logs first, then converting to exponential form — verify with b^y.
- 3
Week 3 · ~20 min/day
Logs in the wild
Goals
- Read Richter, pH and decibel scales
- Choose base 2 / 10 / e for the domain
- Sketch and interpret log curves
Practice
Convert one news headline (quake, pH, sound) into a log statement and back.
Exam tips
- •Combine log terms before exponentiating — one log per side, then flip.
- •Always check the domain last; cross out any root with x ≤ 0.
- •When in doubt, change base to ln and let the calculator do it.
Practice Problems
0/6 solvedTry each problem first, peek at the hint only if stuck, then reveal the solution and mark it solved.
Evaluate log₁₀(10,000).
Evaluate log₂(64).
Condense: log(x) + log(y) − log(z).
Solve log₃(x) = 4.
Solve log_b(125) = 3 for b.
A sound is 100,000× the reference intensity. How many decibels (10·log₁₀)?
Printable Worksheet
Generate a fresh problem set for class or homework. Print it, or copy the answer key separately.
- 1.18 × 47 =
- 2.8 ÷ 11 =
- 3.38 × 26 =
- 4.35 ÷ 4 =
- 5.21 − 16 =
- 6.2 + 26 =
- 7.14 ÷ 12 =
- 8.23 ÷ 3 =
- 9.49 ÷ 7 =
- 10.22 − 17 =
- 11.41 + 18 =
- 12.47 − 35 =
Formula Cheat Sheet
Every formula on this page in one printable table.
| Formula | Meaning | Example |
|---|---|---|
| y = log_b(x) ⟺ x = b^y | Log ↔ exponential flip | log₃(81)=4 ⟺ 3⁴=81 |
| log_b(xy) = log_b(x)+log_b(y) | Product rule | log₁₀(100·1000)=2+3=5 |
| log_b(x/y) = log_b(x)−log_b(y) | Quotient rule | log₁₀(1000/10)=3−1=2 |
| log_b(x^y) = y·log_b(x) | Power rule | log₁₀(100³)=3·2=6 |
| log_b(x) = ln(x)/ln(b) | Change of base | log₅(25)=ln25/ln5=2 |
| log_b(1) = 0 · log_b(b) = 1 | Anchor values | log₂(1)=0, log₂(2)=1 |
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2026-09-29
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