How to Measure With a Tape Measure on Screen

How do I measure something on my screen?

It takes about a minute, and you need any bank card, ID card or store card:

1. Open the actual size ruler and set browser zoom to 100%.
2. Hold the card flat on the screen and move the slider until the outline matches it.
3. Press Save, then lay your object on the glass with one end at zero.
4. Read the length on the inch or centimeter scale.

Why does a bank card work as a reference?

Almost every bank card and ID card follows the same ID-1 standard. It is 85.60 × 53.98 mm (3.37 × 2.13 in), so it is a ruler most people carry.

If you have no card, these standard objects are fixed sizes too:

Which coins can I use to check the ruler?

Coins are good for small checks, since each type has a set diameter.

How do I convert inches to centimeters?

One inch is exactly 2.54 cm, or 25.4 mm. Multiply inches by 2.54 for centimeters, or divide centimeters by 2.54 for inches.

How accurate is a ruler on screen?

With a careful card match, it is close enough for screws, coins and small parts. Look straight at the screen, because viewing at an angle makes the edges harder to line up.

For anything longer than your screen, use a real tape measure.

What can I measure on my screen?

Anything small and flat enough to lay on the glass. Common uses include:

• screws, bolts, nails and washers,
• rings, earrings and watch straps,
• batteries, memory cards and cables,
• coins, stamps and small photos.

Use a soft cloth under anything sharp or metal, so it cannot scratch the screen.

How do I measure a ring on screen?

Lay the ring flat on the ruler and read the inside diameter, from inner edge to inner edge. Read it in millimeters, since ring charts use mm.

Then look up that diameter on your jeweler’s ring size chart. Measure twice, turning the ring a quarter turn between readings.

How do I measure a screw or bolt?

Two numbers describe most screws and bolts. Measure them like this:

1. For length, measure from under the head to the tip. For a flat head that sits flush, measure the whole screw.
2. For thickness, measure across the threads at the widest point.
3. Compare the result with the sizes on the pack or the hardware store’s chart.

For thread sizes under a millimeter apart, a digital caliper gives a much more exact reading than any screen.

How do I measure the size of my screen itself?

Screens are sold by the diagonal of the lit area, not the frame. Our monitor size tool works it out from the same bank card match, with no tape needed.

For a TV, follow our guide on how to measure a TV. For a phone, see how to check your phone screen size.

Why does browser zoom change the ruler?

Zoom makes everything on the page bigger or smaller, including the ruler. Keep zoom at 100% while you match the card and while you measure.

Moving the window to another screen also changes the size, because each screen has its own pixel size. Match the card again on the new screen.

Should I use a ruler, a tape measure or a caliper?

Each tool suits a different job. Pick by the size of what you are measuring:

• On-screen ruler: small flat objects, when no ruler is at hand.
• Tape measure: rooms, furniture, TVs and walls.
• Digital caliper: small parts, to a fraction of a millimeter.

For a TV wall or desk, a tape measure with both inches and centimeters saves you from converting.

How do I check a print or photo size?

Common print sizes are named in inches. Here they are in millimeters too, so you can check them against the ruler:

• 4 × 6 in: 101.6 × 152.4 mm, a standard photo print.
• 5 × 7 in: 127 × 177.8 mm, a common frame size.
• 8 × 10 in: 203.2 × 254 mm, a large print.

Each of these has its own shape. Our guide on how to calculate aspect ratio shows how to crop a photo to fit.

How do I check a paper size?

Hold the paper against the screen after setting the ruler with a card. A4 is 210 × 297 mm, and US Letter is 8.5 × 11 in (215.9 × 279.4 mm).

A full sheet is bigger than most laptop screens are tall. Line up one edge first, then slide the sheet to check the other.

Can I measure on a phone or tablet?

Yes, but a phone screen is small. Turn it sideways so the card fits along the long edge when you set the scale.

For anything longer than the screen, a tape measure is quicker. To find the phone’s own screen size, see how to check your phone’s screen size.

Can I print a ruler instead?

You can, but printers often scale the page. Choose Actual size or 100% in the print settings, never Fit to page.

Check the printed ruler against a bank card before you trust it. The card’s long side should line up with 85.6 mm.

How do I turn pixels into inches or millimeters?

Divide the pixels by your screen’s pixels per inch. For example, 300 pixels on a 96 PPI screen is 300 ÷ 96 = 3.1 in (7.9 cm).

Multiply inches by 25.4 for millimeters. Our PPI calculator finds your screen’s density from its size and resolution.