Online Ruler: Measure Real Size on Your Screen

Free 1:1 ruler in mm, cm and inches. Calibrate once with any bank card.

① CalibrateMatch a bank card once
→
② Place itCoin, ring, screw, photo…
→
Size 27.0 mm 2.70 cm · 1.06 in
③ Read itmm, cm or inches

Example values

More tools

RingRing size finderMatch your ring on screen, get US, UK & EU size 1:1Actual-size objectsBank card, passport photo, SIM, coins Fit?Fit checkerWill it fit in the box, bag or drawer? A4Paper sizesA0 to A6 in mm, cm and inches GameSize guessing gameTrain your eye: guess, then measure DailyDaily challengeOne secret length a day

Everyday uses: parcels, cabin bags, laptops, photos

Courier & Parcel Box Check

Selling on Meesho, Amazon, or shipping via Delhivery? Check if your product fits standard courier boxes or polybags to prevent unexpected volumetric weight fees.

Check Parcel Box

Flight Cabin Baggage (55×35×25 cm)

Avoid ₹3,000+ gate baggage penalties on IndiGo, Air India, SpiceJet, or international flights. Test whether your trolley bag fits standard cabin overhead limits.

Verify Cabin Bag

Laptop Sleeve & Bag Sizing

Buying a backpack or sleeve? Verify if your 13-inch, 14-inch, or 15.6-inch laptop fits with adequate safety margin and corner bumper padding.

Test Laptop Fit

Passport Photo & Card Scale

Inspect 35mm × 45mm passport photos, visa prints, Aadhaar PVC cards, and stamp dimensions directly against your screen with calibrated 1:1 precision.

Open 1:1 Ruler

Ring Size & Hardware Diameter

Place rings, coins, washers, nuts, or bolts directly on the glass to find exact millimeter diameter and circumference without physical calipers.

Measure Diameter

How the ruler stays accurate

Why Calibrating Your Screen Is Essential

Web browsers natively operate in CSS pixels, not real-world units. Because physical screens have vastly differing pixel densities (DPI/PPI)—ranging from around 100 PPI on desktop displays to over 450 PPI on modern mobile screens—a generic CSS centimeter cannot guarantee physical accuracy.

OnlineMeasurer solves this by using the standardized ISO/IEC 7810 ID-1 standard. Any bank card, driver's license, or Aadhaar PVC card in your wallet has an identical length of exactly 85.60 mm (3.37 inches). By matching an outline on your screen to a card, the application computes the exact pixels-per-millimeter ratio (pxPerMm) for your specific hardware.

The 8 Themed Measurement Worlds

The game divides real-world dimension learning into 8 progressive categories:

World 1: Jeb ke Sikke (Pocket Coins) – Common currency coins (₹1, ₹2, ₹5, ₹10) and standard credit cards.
World 2: Battery Bazaar (Batteries & Small Objects) – CR2032 coin batteries, AAA and AA alkaline cells, 9V blocks, and standard playing cards.
World 3: Gadget Dabba (Desk Tech) – Nano SIM cards, USB Type-A plugs, 3x3 Rubik's cubes, and optical discs.
World 4: Kaagaz Mela (Paper Sizes) – ISO 216 paper dimensions from A6 postcards to large A3 sketch sheets.
World 5: Khel ke Gole (Sports Balls) – Standard golf, table tennis, tennis, cricket, and association football balls.
World 6: Note Ginti (Currency Notes) – Subtle length differences among modern Indian banknotes (₹10, ₹50, ₹100, ₹500) and US one-dollar bills.
World 7: Bade Naap (Large Equipment) – Tennis rackets, cricket stumps, maximum legal cricket bats, and doorway clearances.
World 8: Bahut Bade (Courts & Pitches) – Basketball rims, football goalposts, badminton courts, cricket pitches, and regulation tennis courts.