Simple tools. Instant answers.
Free calculators, converters and everyday tools that work instantly in your browser — private, fast and always available.
A reference you can check, not a wall of empty calculators
MultiConvers is an independent collection of calculators and converters for a specific question: a percentage, a unit, a date span, an electricity estimate, a body-mass index. Each tool page states the formula, a worked example and the case the number does not cover.
If you want the method before the widget, start with a guide. How percentages work separates “percent of”, “percent off” and a change between two totals — then the percentage calculator runs the one you meant. Centimetres to inches uses the exact 2.54 definition. Electricity cost is kilowatt-hours times the rate you type. A Nordic bill also has a grid fee and energy tax, which that rate does not include unless you put them there. What BMI measures is the screening ratio and the WHO adult bands, not a diagnosis — the BMI calculator only computes that ratio.
The site is maintained by one person. A page is added when it has its own explanation. Corrections are listed on About.
Popular tools
A short list of tools already showing in search. The rest of the catalog is in the categories below.
kW to HP
Convert kilowatts to mechanical horsepower using 1 hp = 0.7456998716 kW.
MPG to L/100km
Convert miles per gallon to litres per 100 km, choosing US or Imperial gallons explicitly.
HP to kW
Convert mechanical horsepower to kilowatts (1 hp = 0.7456998716 kW).
US Gallons to Liters
Convert US liquid gallons to litres using 1 US gal = 3.785411784 L exactly.
F to C
Convert Fahrenheit to Celsius with C = (F − 32) × 5/9. 32°F is 0°C; 212°F is 100°C.
Right Triangle
From two legs, or a leg and the hypotenuse, get the third side, both acute angles, area and perimeter.
Miles to KM
Convert international miles to kilometres. One mile is exactly 1.609344 km.
BMI Calculator
Compute body mass index from height and weight using kg/m², with WHO adult categories.
Circle Calculator
From radius, diameter or circumference, get the other two plus the area of a circle.
C to F
Convert Celsius to Fahrenheit with the exact formula F = C × 9/5 + 32.
Calculator categories
Math, statistics, geometry, fitness and date tools.
Math
Percentages, roots, fractions, logs and other everyday math made instant.
Statistics
Standard deviation, probability, sample size, z-scores and other everyday stats tools.
Geometry
Area, volume, triangles, circles and distance — with length, area and volume units kept separate.
Fitness
BMI, BMR, calories, pace and training estimates from published formulas — not medical advice.
Date & Time
Calculate dates, ages, durations and business days without touching a spreadsheet.
Conversion categories
Units, energy, driving, utilities, text and developer tools.
Conversions
Convert length, weight, temperature, volume and power between common units.
Energy
Estimate electricity, appliance and EV charging costs before you pay the bill.
Automotive
Fuel cost, fuel economy and trip cost tools for drivers.
Utilities
Password, UUID, encoding, JSON, hash and other tools that run locally.
Text
Word counts, character counts and other text utilities that run locally.
Developer
Unix timestamp conversion and other small lookups developers reach for often.
Recently added
Newer calculators added after the first catalog.
Password Generator
Create a strong random password in your browser. No signup, and the password is never stored or sent to analytics.
UUID Generator
Generate one or many RFC 4122 UUID v4 values in your browser. Copy or download as TXT.
JSON Formatter
Pretty-print, minify or validate JSON in your browser. Parse errors show an approximate line and column.
QR Code Generator
Create static QR codes for URLs, Wi-Fi, text, email, SMS and contacts. Download PNG or SVG in your browser — no signup.
Hash Generator
Hash text with SHA-256, SHA-384 or SHA-512 in your browser. Output is lowercase hex. Hashing is not encryption.
Color Converter
Convert colors between HEX, RGB and HSL with a live preview. Accepts #RGB and #RRGGBB.
Scientific Calculator
Evaluate expressions with powers, roots, logs, factorials and trigonometry in degrees or radians.
Triangle Calculator
Find a triangle’s area, perimeter and angles from three sides, or the area from base and height or SAS.
Browse all tools
106 published tools across 11 categories. Every calculation stays on your device.
Built to be useful
Instant answers
The calculator is at the top of every tool page. No sign-up and no waiting for a server.
Documented formulas
Each page shows the method, worked examples and the limits of the calculation.
Private by default
Values you type stay in the browser. Text tools never send what you paste.