How to hang a picture straight (using your phone as a level)

How high to hang a picture

A widely used rule of thumb, often credited to galleries, puts the centre of a picture about 145 cm (57 in) from the floor. That's roughly the eye level of an average adult standing up. It's a starting point, not a law:

• Above a sofa, sideboard or bed, the furniture matters more. Leave a gap of roughly 15 to 25 cm (6 to 10 in) between the top of the furniture and the bottom of the frame.
• In rooms where people sit, such as a dining room, hang a little lower.
• For a group of frames, treat the whole group as one picture and put its centre at 145 cm.

How to hang a picture straight, step by step

1. Choose the spot. Hold the frame up, or tape a paper template of the same size to the wall, and stand back.
2. Check for cables and pipes. Avoid drilling directly above or below sockets and switches. Use a detector if you're unsure.
3. Mark the hook height with a pencil, using the sum above. Mark the horizontal centre too.
4. For two hooks, mark both at the same height. Lay a long, straight piece of wood or a long ruler between the marks, rest your phone on it, and adjust until it reads 0°.
5. Fix the hook with a fixing that suits the wall and the weight: picture hooks for light frames, plugs and screws for heavy ones.
6. Hang and level. Stand the phone on its long edge along the top of the frame and nudge the frame until the level turns green.
7. Stand back and check by eye. Ceilings, skirting and door frames are not always level, so a picture can be perfectly level and still look wrong beside them. Trust the level, but use your eyes too.

Using your phone as a level

Every modern phone has an accelerometer, a tiny sensor that feels which way gravity pulls. A level app turns that into degrees of tilt. Bubble Level has two modes:

• Surface level. Lay the phone flat on a shelf or table. A bubble shows tilt in two directions at once.
• Edge level. Stand the phone on one of its long edges, like a small spirit level. This is the one for picture frames and shelf edges.

Both turn green with a tick at 0°. You can lock a reading, or set your own zero to match a slope that isn't level, such as a stair rail. On an iPhone, tap Allow motion the first time so the browser can read the sensor.

Phones sit badly on some surfaces. A camera bump rocks the phone when it's flat, and some cases have uneven edges. Take a bulky case off, or calibrate with it on, the way you'll use it.

Calibrating a phone level

A phone's sensor can be slightly off from the factory. The fix is the same trick builders use to check a spirit level:

1. Put the phone on a flat, steady surface and take a first reading.
2. Turn it around end for end (180°), put it back on exactly the same spot, and take a second reading.
3. Let the app work it out. The surface's own slope reverses when you turn the phone, but the sensor's error doesn't, so the difference reveals the error. Bubble Level then takes it out of every reading.

The surface doesn't need to be level for this to work, only steady. Recalibrate if you change case.

How accurate is a phone level?

Accurate enough for most frames, if you calibrate it. The bigger limit is length. A phone is only about 15 cm long, so any small bump or speck under it tilts the whole reading, and it can't see a dip in the middle of a long shelf. This table shows what a small angle means in real life:

So a frame that's half a degree out is about 5 mm higher at one end. To level something longer than your phone, put the phone on a long, straight batten or ruler laid across it. That averages out the bumps.

Measuring small things on your screen

For a quick measurement, such as the gap between D-rings or the size of a small print, an on-screen ruler helps. There's a catch: a browser doesn't know the physical size of your screen, so an uncalibrated on-screen ruler can be noticeably off.

The fix is the bank-card trick. Bank cards, ID cards and most library cards share one size, set by the international standard ISO/IEC 7810 (format ID-1): 85.60 × 53.98 mm. Hold a card flat on the screen and resize the drawn card until it matches. In Bubble Level's ruler you do this once, and it's saved on your device.

An on-screen ruler can only measure what fits on the screen. For a wall, use a tape measure.

When to use a real spirit level

A phone level is handy, and it's always in your pocket. A spirit level is the better tool when:

• the job is longer than about 60 cm: long shelves, worktops, curtain poles, rails
• a few millimetres matter: kitchen units, tiling, flooring, door frames
• you need a true vertical (plumb) for posts or uprights
• you're working outdoors on fences, decking or paving
• it's building or structural work, or anything that bears weight
• you're hanging a long row of frames: a laser level makes that much faster

Bubble Level says the same in the app: phone sensors vary, so calibrate for the best readings and use a proper tool where accuracy matters.

Common mistakes

• Hanging too high. Measure to the centre of the picture, not the top.
• Forgetting the wire drop. The hook goes below the top of the frame, by the distance from the tight wire to the top.
• Levelling with a bulky case on without calibrating with it.
• Trusting the ceiling line. Old houses are rarely square. Level the frame, then check how it looks.
• Drilling without checking for cables. Avoid the areas directly above and below sockets and switches.