Unit Conversion Quick Reference
Convert between metric and imperial units for length, weight, temperature, volume, and area with common reference values.
Percentage Calculator
Calculate percentages, increases, decreases, and ratios
Unit Conversion Reference
Converting between measurement systems is one of the most common everyday calculations. Memorizing a few key conversion factors and reference values makes estimation fast and accurate.
Length
1 inch = 2.54 cm (exact). 1 foot = 30.48 cm. 1 mile = 1.609 km. Quick mental math: multiply miles by 1.6 for km, divide km by 1.6 for miles. Or use the Fibonacci approximation: consecutive Fibonacci numbers approximate the mile/km ratio (5 miles β 8 km, 8 miles β 13 km).
Weight
1 pound = 453.6 grams. 1 kilogram = 2.205 pounds. 1 ounce = 28.35 grams. Quick mental math: double the kg and add 10% for pounds (70 kg β 154 lbs: 140 + 14). For cooking, 1 stick of butter = 113g = 4 oz = 8 tablespoons.
Temperature
Fahrenheit to Celsius: (Β°F - 32) Γ 5/9. Celsius to Fahrenheit: (Β°C Γ 9/5) + 32. Key reference points: water freezes at 0Β°C/32Β°F, boils at 100Β°C/212Β°F. Room temperature is about 22Β°C/72Β°F. Body temperature is 37Β°C/98.6Β°F. For quick estimation: double Celsius, subtract 10%, add 32.
Volume
1 gallon (US) = 3.785 liters. 1 cup (US) = 236.6 mL. 1 tablespoon = 14.8 mL. 1 fluid ounce = 29.6 mL. Note: UK gallons and cups differ from US measurements. 1 UK gallon = 4.546 liters. Cooking volumes also differ between US, UK, Australian, and Japanese standards.
Area
1 square foot = 0.0929 mΒ². 1 acre = 4,047 mΒ² = 0.4047 hectares. 1 square mile = 2.59 kmΒ². For real estate: multiply square meters by 10.76 for square feet. A football field is about 1.32 acres or 0.53 hectares.
κ΄λ ¨ λꡬ
κ΄λ ¨ κ°μ΄λ
How to Use Scientific Notation and Number Formatting
Scientific notation makes very large and very small numbers manageable. This guide covers notation systems, significant figures, and formatting conventions used in science, engineering, and finance.
Unit Conversion Best Practices for Developers
Incorrect unit conversions have caused spacecraft crashes and medical errors. This guide covers best practices for implementing unit conversions in software, including precision handling and common pitfalls.
Percentage Calculations: Common Formulas and Pitfalls
Percentage calculations appear simple but hide common errors, especially around percentage change, percentage points, and compound percentages. This guide clarifies the math behind everyday percentage problems.
Matrix Operations: A Visual Guide for Developers
Matrices are fundamental to graphics, machine learning, and data processing. This guide explains matrix addition, multiplication, transposition, and inversion with visual examples and practical applications.
Troubleshooting Floating-Point Precision Errors
Floating-point arithmetic produces surprising results that can cause bugs in financial calculations, comparisons, and cumulative operations. This guide explains why these errors occur and how to handle them.