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Concave vs. Convex

Concave and convex are most commonly used as adjectives to describe the outline or surface of a shape. The terms aren’t often used in everyday speech, but they are important for use in science and mathematics. You will most likely come across the terms convex and concave when discussing mirrors, lenses in eyeglasses or contact lenses.

What is the Difference Between Concave and Convex?

The basic difference between concave and convex are as follows:
  • Concave describes a shape that curves inwards. The sideview mirror of a car, which curves inwards, is a good example of a concave shape.
  • Convex describes a shape that curves outwards. An (American) football, which curves outwards, is a good example of a convex shape.

When to Use Concave

We most commonly use concave to describe processes linked to lenses, mirrors and reflection. A concave mirror, for example, will make you look taller due to the way light reflects back from it. Concave lenses might be used in things like telescopes, binoculars, cameras and lenses in eyeglasses. You might use concave for less scientific descriptions when describing, for example, something that curves inwards like a crater or pothole, or the stomach of a very thin person. In some rare cases you will see concave used in a descriptive, but non-literal, sense. For example:
  • He lost so much weight around his face that his cheeks have taken on a hollow, concave
In the example above, concave is used in a slightly exaggerated sense, i.e. the shape we are describing might not be technically concave, but the adjective is used loosely as a synonym for thin or sunken in appearance. Concave can be used as a noun in mathematics and geometry, i.e. it is a name for a type of shape or inwardly curved line.

When to Use Convex

As with concave, we mostly use convex to describe processes linked to lenses, mirrors and reflection. A convex mirror will make you look smaller due to the way light reflects back from it. Convex lenses might be used in microscopes, magnifying glasses and eyeglasses. Convex is also used as a noun in in mathematics and geometry, i.e. it is a name for a type of shape or outwardly curved line.

Concave vs. Convex Examples

Here are some examples of concave and convex used in a sentence:
  • The table was not flat, but sloped outwards, slightly convex like the glass of a watch.
  • The corset made her waist look tiny, giving a concave, hour-glass shape to her body.
  • The snowballs were perfectly round, their convex form looking like they had been made with an ice cream scoop.
  • Contact lenses are concave in shape, allowing for a better, sharper image to be seen by the wearer.
  • The baby’s navel was convex, protruding outwards.
  • From our vantage point on top of the mountain, we beheld the concave sloping of the valley sweeping down towards the sea.

Tips To Remember the Difference

The most important thing to remember is that concave means curving inwards and convex means curving outwards. A good tip is to focus on the ‘cave’ part of concave. If you remember that the mouth of a cave curves inwards, then you can remember that concave means bent inwards. As convex – bent outwards – is the opposite of concave, it should be easy to remember.


Convex and concave are two words that describe a line or shape, often in mathematics, science, or in relation to eyeglasses and mirrors. While convex means to bend or protrude outwards, concave is the opposite and means to bend inwards.