Measuring & calculating instruments · EN / FR / AR

Online ruler, unit converters and everyday calculators

Measure the thing. Then do the sums.

A true-to-scale ruler you set up with any bank card, plus a shelf of small converters and calculators for whatever comes next: converting units, splitting a bill, checking what a loan really costs, finding a ring size. Nothing you type is sent to us.

Scale
1:1 after calibration
Resolution
0.5 mm · 1/16 in
Reference
ISO ID-1 card, 85.60 mm
Instruments
19
Languages
EN · FR · AR
Fig. 1 · Live rulerSpan: 8.56 cm · 85.6 mm · 3.37 inCalibrate in 20 seconds →

Drag along the strip to measure a span. Until you calibrate, treat it as a good guess, not gospel.

The catalog

19 instruments. Each one does a single job, shows its work, and never asks for your email.

  1. Online RulerTrue-scale cm, mm and inches, calibrated with a bank card
  2. Unit ConverterLength, weight, temperature, area, volume: every unit at once
  3. Percentage CalculatorShares, ratios and percent change, in three lines
  4. BMI CalculatorBody mass index from kg and cm, or lb and ft/in, with WHO bands
  5. Loan / EMI CalculatorMonthly payment, total interest, first-year schedule
  6. Age CalculatorExact age to the day, plus the countdown to the next cake
  7. Date DifferenceDays, weeks and months between two dates
  8. Tip & Discount CalculatorSplit a bill with a tip, or see the real sale price
  9. Ring Size ConverterUS, UK and EU ring sizes from a diameter in mm
  10. Shoe Size ConverterEU, UK and US shoe sizes from foot length
  11. Paper SizesA4, Letter and friends in mm, inches and pixels
  12. Inches to cmAny length in inches, fractions included, plus a 1–48 in chart
  13. cm to inchesDecimals and the nearest 1/16 in, with a 1–100 cm chart
  14. Feet to cm (height)Height in feet and inches to cm and back
  15. mm to inchesMillimeters to decimal and fractional inches
  16. Screen Size & PPIPixel density and the real width and height of a screen
  17. Paper Size in PixelsA4, Letter and friends in pixels at any DPI
  18. Circle & Area CalculatorRadius, diameter, circumference, area, and rectangles
  19. Cooking ConverterCups to grams and ml for common ingredients

Field notes

Short guides for the days when the proper tools are in another drawer.

  1. How to measure without a rulerCards, coins, banknotes and your own thumb, ranked by how much to trust them
  2. How to find your ring size at homeThree ways to measure: a ring that fits, a strip of paper, or the on-screen ruler.
  3. How long is an A4 sheet in cm and inches?21 × 29.7 cm, 8.27 × 11.69 in, and why the ratio is √2
  4. How to measure your screen sizeThe diagonal, in inches, without the frame, and what it means in cm
  5. Common objects that measure about 1 inch or 1 cmCoins, batteries and cards to picture 1 in and 1 cm