Our calibrated screen ruler is great for anything that fits on your screen: a screw, a coin, a ring, a business card. But a phone screen is only about 15 cm long. To measure a sofa, a window, a wrist or a 3D-printed part to a tenth of a millimetre, you need a physical tool.
Below is the tool we'd reach for in each situation, and what to look for when you buy one. Prices on Amazon change often, so we link to current listings instead of quoting a price.
| What you're measuring | Best tool | Typical accuracy |
|---|---|---|
| Small items on screen (coins, rings, cards) | Screen ruler (free) | ±1 mm after calibration |
| Furniture, doors, cupboards | Tape measure | ±1 mm |
| Rooms, ceilings, long distances | Laser distance measure | ±1.5–3 mm |
| Screws, jewelry, small parts | Digital caliper | ±0.02–0.03 mm |
| Body, clothing, curved surfaces | Soft sewing tape | ±1–2 mm |
| Finger size for rings | Ring sizer | Half a ring size |
| Gardens, driveways, plots | Measuring wheel | About 0.1–0.5% of distance |
1. A 25 ft (7.5 m) tape measure
If you only own one measuring tool, make it this. Look for a blade marked in both inches and centimetres, a wide blade (about 1 inch / 25 mm) that stays straight when extended, a lock button, and a belt clip. A true-zero hook that slides slightly lets you measure accurately both inside and outside an edge.
See tape measures on Amazon2. A laser distance measure
Point, press, read. A laser measure gives you wall-to-wall distances in a second without a helper, and most compact models reach 30–50 m. Useful extras are area and volume modes (handy for paint and flooring) and a backlit screen. Bosch, DeWalt and many smaller brands make good entry-level models.
See laser measures on Amazon3. A 6-inch digital caliper
A caliper measures outside size, inside size and depth, usually to 0.01 mm. A 150 mm / 6-inch stainless-steel model covers almost every small object. Look for a large display, an mm/inch toggle button and a zero button so you can measure differences. Avoid all-plastic calipers if you want them to stay accurate.
See digital calipers on Amazon4. A steel ruler with metric and inch markings
A flat 12-inch / 30 cm stainless-steel ruler is more accurate than a plastic school ruler, doesn't warp, and doubles as a cutting edge. A cork back stops it sliding on paper. It's also the easiest way to double-check your screen ruler's calibration.
See steel rulers on Amazon5. A soft sewing tape
For a waist, chest, wrist or the outside of a round object, a rigid tape is useless. A 60-inch / 150 cm fibreglass sewing tape bends around curves without stretching. Some come in a retractable case, which keeps them from tangling in a drawer.
See sewing tapes on Amazon6. A ring sizer
Our ring size finder works well if you already have a ring that fits. If you don't, a reusable plastic ring sizer (a strip or a set of loops) measures the finger itself. Jewelers use a metal finger-gauge set and a ring mandrel for the most accurate result.
See ring sizers on Amazon7. A measuring wheel
For distances longer than a tape measure, walk a measuring wheel along the line and read the counter. Larger wheels (about 12 inches / 30 cm) roll more smoothly over grass and gravel. Most fold down for storage.
See measuring wheels on AmazonTips for getting accurate measurements
- Measure twice. Write the number down straight away, then measure again before you cut or buy.
- Measure the inside opening, not the outside frame, when checking if something will fit. Our fit guide explains how much margin to leave.
- Keep the tape straight and level. A sagging tape over a long distance always reads too long.
- Check your units. Many tapes and calipers switch between inches and mm. Use our inches to cm chart if you need to convert.
Measuring something small?
You might not need a tool at all. Calibrate your screen once with a bank card and measure it for free.
Open the Online RulerFrequently Asked Questions
Is a screen ruler as accurate as a real ruler?
After calibrating with a bank card, an on-screen ruler is accurate to about a millimetre for items that fit on your screen. For anything longer than your screen, or when you need tenths of a millimetre, use a physical tape measure or caliper.
Laser measure or tape measure for measuring a room?
A laser measure is faster for wall-to-wall distances and ceilings, and you can use it alone. A tape measure is better for short lengths, inside cabinets and anything you need to measure around.
What is the most accurate tool for measuring small objects?
A digital caliper. Most read to 0.01 mm (0.0005 in) and measure outside size, inside size and depth, which makes them ideal for screws, jewelry, coins and 3D-printed parts.