Percentage Calculator
Calculate percentages quickly and accurately. Find what percent one number is of another, calculate percent increase or decrease, and more.
Open ToolEveryday Math Tools
Quick calculators for common math tasks. Calculate percentages, find differences between numbers, and solve everyday calculations without the hassle.
Unit Converter
Convert units for length, weight, temperature, area, volume, speed, time, and data. Get instant results with formulas and quick equivalents.
Open ToolYour Complete Guide to Everyday Math Calculations
Mathematics is woven into daily life in ways most people do not think about. Every time you calculate a tip, compare prices, figure out a discount, convert a recipe measurement, or check how much data your phone plan includes, you are doing math. The tools on this page are designed for exactly these situations: real-world calculations that need to be fast, accurate, and hassle-free.
This guide explains what each tool does, the math behind common calculations, and practical tips for using percentages and unit conversions effectively. Whether you are shopping, cooking, budgeting, or working on a project, these calculators turn numbers into useful answers.
Understanding Percentage Calculations
Percentages are everywhere: sale prices, tax rates, interest rates, exam scores, nutritional labels, survey results, and statistics in news articles. The core concept is simple: a percentage represents a fraction of 100. "25%" means 25 out of 100, or one quarter. But applying percentages to real numbers is where most people slow down or make errors.
Our Percentage Calculator handles the three most common calculation types. First, "What is X% of Y?" answers questions like "What is 15% of $85?" for calculating tips or tax. Second, "X is what percent of Y?" answers questions like "I scored 42 out of 50. What percentage is that?" Third, percentage increase or decrease answers questions like "The price went from $80 to $100. What is the percentage increase?"
When Percentages Matter Most
Percentages are critical in financial decisions. A 2% difference in a mortgage interest rate can mean tens of thousands of dollars over the life of a loan. A "50% off" sale sounds great, but if the original price was inflated, the actual savings may be less impressive. Understanding percentage calculations helps you see through marketing and make informed decisions.
- Shopping: Comparing prices after discounts, calculating sales tax, determining final cost
- Finance: Interest rates, investment returns, salary increases, budget allocations
- Academics: Exam scores, grade calculations, improvement tracking
- Health: Body fat percentage, nutritional breakdowns, medication dosage adjustments
- Business: Profit margins, growth rates, market share, conversion rates
Unit Conversions Explained
The world uses multiple measurement systems, and switching between them is a constant source of confusion. The metric system (meters, kilograms, Celsius) is standard in most countries, while the imperial system (feet, pounds, Fahrenheit) is common in the United States. Our Unit Converter bridges this gap across eight categories: length, weight, temperature, area, volume, speed, time, and data storage.
Most conversions are simple multiplications. One inch equals 2.54 centimeters. One kilogram equals 2.205 pounds. One mile equals 1.609 kilometers. Temperature is the exception because it involves both a multiplier and an offset: Fahrenheit = (Celsius x 9/5) + 32. Our converter applies the correct formula automatically and shows you the conversion path in the details panel.
Data Size Conversions
Digital storage is a growing area of confusion because two competing standards exist. The decimal system uses powers of 1000 (1 KB = 1,000 bytes), which storage manufacturers prefer because it makes drives appear larger. The binary system uses powers of 1024 (1 KB = 1,024 bytes), which is how operating systems actually allocate storage. This discrepancy is why a "500 GB" drive shows less than 500 GB when you connect it to your computer. Our converter uses the binary system (1024) for practical computing accuracy.
Tool Comparison
| Tool | What It Calculates | Inputs Needed | Best For |
|---|---|---|---|
| Percentage Calculator | Percentage of a number, percent change, ratio | Two numbers | Shopping, finance, grades, statistics |
| Unit Converter | Conversions across 8 unit categories | Value, from unit, to unit | Cooking, travel, projects, computing |
Common Mistakes to Avoid
The most frequent percentage error is confusing percentage points with percentages. If an interest rate goes from 3% to 5%, it increased by 2 percentage points but by 66.7% in relative terms. News reports often mix these, leading to misunderstandings. Another common mistake is applying percentage changes sequentially: a 50% increase followed by a 50% decrease does not return you to the original value. If $100 increases by 50% to $150, then decreases by 50%, the result is $75, not $100.
For unit conversions, the most common error is confusing similar units. A fluid ounce is not the same as a weight ounce. A US gallon (3.785 liters) is not the same as an imperial gallon (4.546 liters). Our converter labels units clearly to avoid these mix-ups.
Privacy and Accuracy
Both tools run entirely in your browser. Your numbers are never sent to any server or stored in any database. The percentage calculator uses exact arithmetic. The unit converter uses standard conversion factors recognized by international measurement authorities. For cooking measurements like cups, slight regional variations exist, which the tool notes in its results.
Frequently Asked Questions
How do I calculate a discount price?
Use the "What is X% of Y?" mode. Enter the discount percentage and the original price. Subtract the result from the original price to get the final price. For example, 20% of $50 is $10, so the discounted price is $40.
Why does the temperature conversion use a different formula?
Most unit conversions are simple multiplications (multiply by a factor). Temperature has both a scale difference and an offset: Fahrenheit uses a different zero point and different degree size than Celsius. The formula accounts for both: F = (C x 9/5) + 32.
Is 1 KB equal to 1000 or 1024 bytes?
Both definitions exist. Marketing and storage manufacturers use 1000 (decimal). Operating systems and computing use 1024 (binary). Our converter uses 1024 for practical computing accuracy.
Can I use these calculators offline?
Once the page has loaded, the calculations run locally in your browser and do not require an internet connection.
Is my data stored?
No. All calculations happen locally. Your inputs are not sent to any server or stored after you close the page.
How accurate is the unit converter?
The converter uses standard conversion factors. You can increase precision to 6 decimal places for scientific work. For everyday use, 2-3 decimal places are more than sufficient.