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Finance, health, math, science, unit conversion, business, food, sports, education, and daily planning. Every calculator includes the tool, formula notes, examples, FAQs, and related guides.

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Browse by topic area

Five calculator collections

Every calculator is organised into one of five topic areas. Click a collection to browse all the tools, sub-categories, and guides it contains.

Finance

137 calculators

Loans, mortgages, savings, investments, tax, budgets, retirement planning and more.

Finance
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Health & Fitness

385 calculators

BMI, calories, nutrition, body composition, fitness training, sports and wellbeing.

HealthSportsFood
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Science & Engineering

755 calculators

Physics, chemistry, construction, unit conversion, technology and technical design.

ConstructionConversionPhysicsChemistryEngineeringTechnology
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Business & Data

252 calculators

Profit margins, ROI, pricing, statistics, payroll, revenue and business planning.

StatisticsBusiness
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Everyday Life

491 calculators

Math, dates, discounts, tips, education, ecology and everyday household decisions.

MathEveryday LifeEcologyEducation
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Browse by category

Calculator categories

Each category page works like a focused mini-library with topic clusters, descriptions, internal links, and calculator pages targeting specific search intent.

Finance

Plan loans, savings, investments, taxes, budgets, interest, and everyday money decisions with clear formulas and examples.

137 calculators

Health

Estimate health, fitness, nutrition, body measurements, and wellness metrics using practical reference formulas.

135 calculators

Math

Solve percentages, ratios, fractions, averages, geometry, algebra helpers, and common school or workplace math problems.

131 calculators

Construction

Estimate materials, areas, volumes, costs, paint, concrete, flooring, roofing, and renovation quantities.

130 calculators

Conversion

Convert units for length, weight, temperature, speed, volume, area, pressure, energy, and daily measurements.

125 calculators

Physics

Work with speed, force, energy, motion, electricity, waves, pressure, and classroom science formulas.

125 calculators

Chemistry

Use chemistry helpers for concentration, molarity, dilution, gas laws, molecular mass, and lab calculations.

125 calculators

Statistics

Analyze averages, probability, samples, confidence, variation, scores, and data interpretation problems.

125 calculators

Business

Estimate profit, margins, markup, inventory, payroll, pricing, revenue, productivity, and business planning metrics.

127 calculators

Everyday Life

Quick calculators for dates, time, tips, discounts, travel, fuel, recipes, shopping, and household planning.

110 calculators

Sports

Calculate pace, performance, training zones, scores, ratios, sports statistics, and fitness planning numbers.

125 calculators

Food

Scale recipes, estimate calories, cooking conversions, ingredient weights, nutrition, and meal planning quantities.

125 calculators

Ecology

Estimate energy use, water use, carbon footprint, recycling, transport impact, and sustainable living metrics.

125 calculators

Engineering

Work through mechanical, electrical, civil, and systems engineering formulas for practical design checks.

125 calculators

Education

Support learning with grade, score, GPA, reading, study time, classroom math, and academic planning calculators.

125 calculators

Technology

Estimate bandwidth, storage, download time, screen sizes, data transfer, battery life, and computing metrics.

125 calculators

Accuracy and transparency

Why United Calculator

Every page follows the same content standard: formula derivation, a worked example with real numbers, applicable laws or professional guidance, 6 plain-language FAQs, and links to 8 related tools.

Verified formulas

Each formula engine is based on published standards — TILA for loan calculations, METS tables for energy expenditure, ASTM standards for materials, and equivalents across 16 subject areas. The formula is shown in a code block on every result card so you can verify the calculation independently.

Professional context, not professional advice

Finance and health calculators cover applicable legislation (CFPB, NHS, OSHA) and reference professional thresholds (e.g. debt-to-income ratios accepted by lenders, WHO BMI categories). Every page includes a disclaimer — these tools are planning aids. Consequential decisions should be reviewed with a qualified professional.

No account, no tracking, no fee

Calculations run entirely in your browser. No data leaves your device. There are no login walls, no usage limits, no subscription tiers, and no premium paywalls. The only data stored is nothing — no cookies are set beyond what your browser requires to render the page.

Transparent methodology

Smart defaults come from published benchmarks — median UK household income from ONS, US average mortgage rate from Freddie Mac weekly surveys, average commute distances from the US Census ACS. Defaults are documented in the article body on each calculator page.

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Simple by design

How United Calculator works

Three steps from question to answer — no account, no subscription, no ads cluttering the result.

Search or browse

Type a topic into the search box or click a category. Each category is a mini-library of 125 calculator pages targeting specific questions — loan payments, BMI, tile counts, carbon footprint, and more.

Enter your values

Smart defaults are pre-filled so you get an immediate example result. Replace any field with your own data. Click the ? icon on any field for a plain-language explanation of what that input means.

Read, copy, and share

The result updates in real time. The formula is shown in a code block below the answer. Copy the result to your clipboard, share it to 8 social platforms, or scroll down for the full explanation, FAQs, and 8 related calculators.

Radioactive Decay Calculator

Radioactive Decay Calculator — calculate radioactive decay with the correct physics formula. Worked example and unit notes included.

An area calculator computes the two-dimensional space enclosed by a geometric shape — essential for construction materials estimation, landscaping, flooring, painting, tiling, and land measurement. Different shapes require different formulas, but all area measurements share a common unit: the square of the length unit used (square metres, square feet, square kilometres, acres, etc.). Getting area calculations right before ordering materials saves significant time and money — the cost of over-ordering tiles or under-ordering insulation material has a direct impact on project budgets. and are useful companion tools for related building and quantity calculations.

Area calculations appear everywhere from school mathematics to professional surveying, architecture, and engineering. Agricultural land in the UK is measured in hectares (1 ha = 10,000 m²) or acres (1 acre = 4,047 m²); residential rooms in square metres or square feet; property in the US in square feet; and road surfaces in square metres. The same formula works regardless of the unit — only the output unit changes.

  1. Select the shape you need to measure: rectangle, circle, triangle, trapezoid, ellipse, or parallelogram.
  2. Measure all required dimensions accurately — use a laser measure for large rooms or a surveyor's tape for outdoor spaces.
  3. Enter the dimensions and select your preferred units (metres, feet, inches, or centimetres).
  4. Read the area in your selected unit and in the automatically converted equivalents (m², ft², acres).
  5. For irregular spaces: divide the area into regular sub-shapes, calculate each, and add them together.
  6. Add a waste allowance for flooring, tiles, or other cut materials — 10% for rectangular rooms, 15–20% for rooms with complex cuts or angles.

Area formulas for common shapes

Rectangle: A = length × width. Square: A = side².

Circle: A = π × radius² ≈ 3.14159 × r². Ellipse: A = π × a × b (semi-major × semi-minor axis).

Triangle: A = ½ × base × height. Alternative (Heron's formula): A = √[s(s−a)(s−b)(s−c)] where s = (a+b+c)/2.

Trapezoid: A = ½ × (a + b) × height, where a and b are the parallel sides.

Worked example: an L-shaped room. Split into two rectangles: 4m × 5m = 20m² and 3m × 2m = 6m². Total = 26m². For flooring with 10% waste: 26 × 1.10 = 28.6m² to order.

Understanding your area result

Area unit conversions and benchmarks

Key conversions: 1m² = 10.764 ft²; 1 ft² = 0.0929 m²; 1 acre = 4,046.86 m² = 43,560 ft²; 1 hectare = 2.471 acres = 10,000 m²; 1 square mile = 640 acres = 2.59 km². Property benchmarks (UK): average new-build flat ~55m²; average terraced house ~88m²; typical detached house ~140m². A typical football pitch is approximately 7,140m² (100m × 71.4m average). A tennis court is 260.75m² (singles) or 298.17m² (doubles).

Physics tips and best practices

Common mistakes to avoid

Area calculations produced by this tool are for planning and estimation purposes only. Structural, planning, and construction measurements for regulated works must be carried out by qualified surveyors under the relevant building regulations (Building Regulations 2010 in England/Wales, equivalent in Scotland and Northern Ireland). Planning applications require professional drawings and certified measurements. Land Registry boundaries are the legal reference for property extents — this calculator does not produce legally certified survey results.