If you need to measure something on the fly, the Measure app on your iPhone has your back.

Thanks to augmented reality (AR), you don't have to wonder if that couch will fit in your living room; you can measure it right at the yard sale. You can even save an image of the object with its dimensions labeled.

It's not quite time to throw away your tape measure, however. The app takes some getting used to, and it's easy to get an inaccurate measurement if you're not holding your phone at just the right angle.

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How to measure the dimensions of an object with your iPhone

Here's what you need to do to measure a 3D object with your phone.

1. If you don't have the Measure app, download it from the App Store. It's made by Apple, so it should be the first to appear when you search "Measure."

2. Once downloaded, tap the Measure app icon to open it.

3. You'll see a box with open corners and an instruction to move your phone around.

4. Move your phone until the AR technology gets its bearings. When that happens, you'll see a circle with a dot in the center.

2 move dot to starting point
2 move dot to starting point
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5. Move your phone until the dot appears on top of the spot you want to measure from.

6. Tap the + near the bottom of the screen.

7. Move your phone slowly until the dot appears above end point of your measurement. You'll see a dotted line to help you keep your measurement on track.

3 measure a line
3 measure a line
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8. When you reach the end point, tap the + again. Your measurement will appear, showing how much distance there is between the two points you set down.

4 save measurement
4 save measurement
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9. If you didn't get the start and end points lined up just right, you can fiddle with the measurement. Put your finger on the endpoint you want to move, and move your finger to reposition the dot.

10. To save an image of your measurement, tap the circle toward the bottom right side of the screen. This saves a photo to your phone.

If you're measuring a couch or other 3D object, you may need to know more than one dimension. The Measure app lets you keep going after your first measurement.

1. With the initial measurement still on your screen, position the dot at one of the points currently in your first line.

2. Tap +.

3. Move your phone so the dot makes a line to the endpoint of your second measurement. Tap + when you get there.

4. Both measurements now appear on your screen. You can add as many measurements as you want. You can also clear your most recent measurement by hitting the back arrow. Tap Clear to remove all the measurements.

5 meaure two dimensions
5 meaure two dimensions
Laura McCamy/Business Insider

5. You can take more photos after you add more dimensions by tapping the white dot on the lower right side of the screen.

How to measure a rectangle and calculate its area

If you hold your phone over a flat rectangular object, the Measure app can measure the outside dimensions and the square inches with one tap.

1. With the Measure app open, position your phone in front of the object and move until the + appears at the bottom.

2. A dotted line will appear around the object.

6 measure a rectangle
6 measure a rectangle
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3. Tap the + or the object and the measurements of the entire rectangle will appear automatically.

7 measure a rectangle
7 measure a rectangle
Laura McCamy/Business Insider

4. You can save a photo of this measurement, too.

One caveat about this function: it took several tries to get the app to return the right dimensions for an 8.5" x 11" piece of paper. The angle of your phone can affect the reading, and distort the measurements. Always measure twice.

How to use your iPhone's Measure app as a level

A level is a handy tool that helps you create flat surfaces and hang picture frames straight. The Measure app has one of those, too. The level function in the app helps you level an upright object or a flat surface.

Here's how to level an upright object, such as a frame hanging on a wall.

1. Tap Level at the bottom right of the Measure app.

2. Place the edge of your iPhone on the top edge of the frame or other object.

3. The number in the center tells you how many degrees off from vertical you are.

4. Adjust the object, with your phone on top, until the number becomes zero. The screen will turn half green.

9 vertical level at 0
9 vertical level at 0
Laura McCamy/Business Insider

Here's how to level a flat surface.

1. Tap Level at the bottom right of the app.

2. Place your iPhone flat on the surface.

3. The number in the center tells you how off you are from vertical. Two white circles move closer or farther to help you find vertical in all directions.

4. When you get to vertical, the screen will turn green and 0 will appear in the center of the circle.

11 flat levet at 0
11 flat levet at 0
Laura McCamy/Business Insider

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