Calculators
From pricing a product to planning a project, turn everyday inputs into a useful estimate.
Features & who it helps
- Business & pricing
- Engineering & materials
- Dimensions & logistics
Good for: Makers, technicians & small-business owners.
For work, curiosity & play.
Tools, data
& a little fun.
Free tools, useful information, and engaging experiences for everyday life.
Explore, learn, create, and play — all in one place.
TOOLS, DATA & PLAY
Explore 4ool
9 free services for work,
curiosity, and play.
Tools & Utilities
Get practical tasks done with calculators and everyday utilities.
QR Tools
Create QR codes for links and guest Wi-Fi, read saved QR images, and prepare printable cards.
Features & who it helps
- URL & Wi-Fi QR codes
- Image downloads & QR reader
- Printable cards & labels
Good for: Small businesses, event hosts & everyday sharers.
Image Tools
Compress, resize, crop, and convert JPG, PNG, and WebP images, or inspect their dimensions and metadata.
Features & who it helps
- Compression & resizing
- Cropping & format conversion
- Image & EXIF information
Good for: Creators, small businesses & anyone preparing images to share.
VIN Decoder
Decode a VIN and explore available vehicle specifications, fuel-economy estimates, recall campaigns, and safety information.
Features & who it helps
- 17-character VIN decoding
- Vehicle specifications
- Available recall & fuel data
Good for: Vehicle owners and people researching a used car.
Play & Explore
Make time for curiosity, puzzles, and interactive experiences.
Logic & Number Puzzles
Play unlimited logic and number puzzles at your own pace.
Sudoku · Pipes · Takuzu · Nonograms · Shikaku · Hashi
Unlimited play · Multiple difficulty levels
Who it helps
Good for: Beginners and puzzle enthusiasts who enjoy solving a challenge with logic.
Astrology
Read daily sun-sign horoscopes and explore the planetary positions behind traditional Western astrology interpretations.
Features & who it helps
- Today & tomorrow’s horoscopes
- Zodiac sign guides
- Today’s planetary positions
Good for: Readers interested in astrology and personal reflection.
Lotto
Generate Korean Lotto 6/45 number sets, revisit a personal seed, and check published draw results.
Features & who it helps
- Random number sets
- My Seed generation
- Draw results & statistics
Good for: Adults exploring Lotto 6/45 number tools and probability.
Data & Insights
Explore and understand public data, from country comparisons to regional statistics.
World Data
Explore country profiles, compare indicators, and follow the numbers behind a changing world.
Features & who it helps
- Country comparisons
- Indicator rankings
- Historical trends
Good for: Students, researchers & curious minds.
Korea Data
Explore South Korea’s registered population, from the national picture to individual regions.
Features & who it helps
- Monthly population
- Regional profiles
- Population & growth rankings
Good for: Researchers, local planners & Korea watchers.
READ BEFORE YOU REACH A CONCLUSION
Featured guides.
Worked examples, common mistakes,
and a clearer idea of what comes next.
Margin vs. markup: choosing the right percentage
Work through a $100 cost and $150 selling price, convert margin to markup, and check how discounts change the result.
Related service: CalculatorsRead the guideGDP vs. GDP per capita: what are you comparing?
Choose between economic size and output per person, compare matching years, and distinguish current dollars from constant prices and PPP.
Related service: World DataRead the guideUnderstanding Korea's administrative regions
Read province, city, county, and district labels correctly, avoid overlapping totals, and match geographic boundaries before comparing statistics.
Related service: Korea DataRead the guideQR Codes vs Barcodes: When to Use Each
Choose between a QR code, Code 128, and EAN by the information, scanner, and workflow you need—not by how the symbol looks.
Related service: QR ToolsRead the guideHow Daily Horoscopes Work
Understand Sun signs, planetary positions, solar houses, and aspects—and read a daily horoscope as reflection rather than a prediction.
Related service: AstrologyRead the guideHow Lottery Odds Work
Understand combinations, the 1 in 8,145,060 jackpot probability for Korean Lotto 6/45, and why past draws do not make a number due.
Related service: LottoRead the guideHow VIN Decoding Works
Read the main parts of a 17-character VIN, understand manufacturer and model-year information, and recognize the limits of a check digit or missing result.
Related service: VIN DecoderRead the guideChoosing an Image Format: JPG, PNG, or WebP?
Choose a format for photos, screenshots, and transparent graphics by comparing compatibility, detail, transparency, and the file actually produced.
Related service: Image ToolsRead the guideSTART WITH YOUR SITUATION
What can you do with 4ool?
Working out a price, quantity, or engineering value?
Choose a formula by the answer you need, not just the numbers you have. A profit margin uses selling price as its denominator; a markup uses cost. For a material estimate, record the shape, measurement unit, and any allowance separately so you can see which assumption changes the result.
Example task: estimate a concrete slab’s volume, then consider an explicit waste allowance.
Open CalculatorsComparing countries without mixing unlike numbers?
Start with one indicator and a shared observation year. A larger total GDP and a higher GDP per person answer different questions. Before drawing a conclusion from a ranking, check whether values use the same unit and year, and whether a blank observation has been mistaken for zero.
Example task: compare two country profiles, then check a per-person measure for the same year.
Open World DataLooking beyond South Korea’s national population total?
Use a regional profile when you need a place over time, or a ranking when you need several places in one period. Compare the same administrative level and population definition. A province and a city inside it overlap; adding both would double-count some residents.
Example task: compare a city’s registered population with the same month a year earlier.
Open Korea DataSharing a link or Wi-Fi details on paper?
Choose a QR type that matches the information you want to share. A URL code opens a destination; a Wi-Fi code contains network details. Keep a clear border around the symbol, print a sample at its actual size, and try it under the lighting where people will use it.
Example task: make a guest Wi-Fi card and test it with a phone before making copies.
Open QR ToolsWant a daily reading with some context?
Astrology offers a traditional symbolic interpretation of planetary positions and angles. Read a sun-sign horoscope as a broad prompt for reflection, rather than a personal forecast or evidence about what will happen. Our guides explain the vocabulary so the interpretation is easier to follow.
Example task: read today’s horoscope, then learn what a square or trine means in that tradition.
Open AstrologyCurious about number sets and lottery probability?
The Korean-language Lotto service offers number generation and a record of draws. A seed is a way to reproduce a selection under the same settings; it does not make that selection more likely to win. Treat past results as history and keep probability separate from pattern-finding.
Example task: compare a random set with a seeded set and explain why their draw odds are equal.
Open LottoTrying to understand a vehicle before researching further?
A VIN decoder can identify attributes reported for an identifier, with coverage depending on the vehicle and data source. A match is a starting point for checking specifications. Accident records, ownership changes, and whether a particular recall repair was completed require different evidence.
Example task: check decoded model information, then separate it from questions for a vehicle history report.
Open VIN DecoderPreparing an image for a website, listing, or message?
Start with the destination’s pixel dimensions, file-size limit, and accepted formats. Resizing changes how many pixels an image contains; compression changes how those pixels are stored. Keep the original, preserve transparency when you need it, and inspect text and fine edges in the downloaded result.
Example task: resize a product photo to the required width, then compress a copy to fit an upload limit.
Open Image ToolsReady for a puzzle at your own pace?
Choose from six logic and number puzzles, then pick an available difficulty that suits you. Start by reading the rules and looking for a move you can explain. With unlimited play, you can practice a technique or try another puzzle whenever you like.
Example task: find a Sudoku cell with only one possible digit before making your next move.
Open Logic & Number PuzzlesFIND YOUR NEXT STEP
Useful starting points.
Calculate, explore, create, or play.
Choose a place to begin.
Calculators
Profit margin
Understand the margin between cost and selling price.
World Data
Compare countries
Compare two countries using shared observation years.
Korea Data
South Korea population
Start with the national resident registration series.
QR Tools
URL QR generator
Turn a website link into a downloadable QR code.
Astrology
Today’s horoscope
Choose a zodiac sign for a reading intended for entertainment and reflection.
Lotto
Number generator
Create a valid number set; generation does not improve the odds.
VIN Decoder
Decode a VIN
Read available specifications from an identifier; this is not a vehicle history report.
Image Tools
Compress an image
Reduce image file size and compare the result before downloading.
Logic & Number Puzzles
Sudoku
Fill each row, column, and box using logic, one number at a time.
A METHOD YOU CAN REUSE
How to choose the right tool.
- 01
Name the question
Write the result you need in one sentence. “How much material?” needs dimensions and units. “Which country has a higher living standard?” needs several measures and careful limits, not one headline total.
- 02
Check what goes in
For calculations, confirm units and quantities. For statistics, match the period, geography, and definition. For a QR code or VIN, verify the exact characters: a perfectly processed input can still be the wrong input.
- 03
Decide what the answer can support
Keep assumptions and source notes with the result. A decoded VIN is not an accident record, and an astrology reading is not scientific evidence. If a result will inform a consequential decision, verify it with the appropriate original source.
KEEP THESE CHECKS HANDY
Useful resources.
Small checks that make a result
easier to trust and reuse.
Before quoting a statistic
Keep the indicator, place, observation period, and source together. Check a common year before comparing “latest” figures.
Compare data consistentlyBefore printing a QR code
Check the link, preserve the blank border, and test the final print at actual size. A crisp screen preview does not prove a small printed code will scan.
Use the printing checklistBefore trusting vehicle information
Separate decoded specifications from a vehicle’s history. A known model or a recall campaign match cannot establish an individual car’s condition.
Know the limits of decodingBefore uploading an image
Check the required pixel dimensions and file-size limit separately. Keep an original copy, then inspect the resized or compressed result at the size people will see.
Choose the right image adjustmentTHE 4OOL APPROACH
For work,
curiosity & play.
4ool brings together free practical tools, useful data, and engaging experiences for work, curiosity, and play. Explore a question, prepare something to share, or settle into a puzzle at your own pace.
Our guides add context with worked examples and source notes. They help you understand a result, choose a method, or learn a solving technique before you try it.
Read about our approach