The Powerful Relationship Between Size Constancy Psychology, Relative Size Psychology & Pricing Psychology

Size Constancy Psychology Applies to Pricing Psychology
Size Constancy Psychology Applies to Pricing

We’re going to take a look at the powerful relationship between Size Constancy Psychology, Relative Size Psychology and Pricing Psychology.

Specifically, how the human brain interprets the size and distance of objects and how it can be fooled into believing that the price of a product or service is higher or lower than what it actually is.

What is Size Constancy Psychology?

Size Constancy Psychology studies how our brain estimates object size accurately.

This might not sound relevant to a B2B or B2C business… But hear me out.

When you think about it, we rely on our brains to estimate the size and distance of objects all of the time.

Something as basic as picking up a cup with our hand or typing on a keyboard would be a very tricky task.

Size constancy psychology is the phenomenon whereby we perceive objects as being of a relatively constant size, despite the fact that the size or distance of the objects varies greatly.

As humans, this phenomenon is important because it allows us to accurately judge the size of objects in our environment.

As we are always on the move, our brain has to compensate for changes in retinal image size due to differences in viewing distance.

This effect is referred to as size constancy and it applies equally to objects and scenes viewed from different distances and directions.

So let’s take a moment to break this down.

When we look at objects, our subconscious estimates it’s size.

In order for our brain to do this, it uses the size of one object as a point of reference and then uses this information to determine the size of another object.

Should the viewing distance from the object change, then our brain adjusts the size of the object accordingly.

How do Depth Cues and Size Cues gather information about distance?

It is believed that in order for our brain to estimate distance, it combines two sensory cues: depth cues and size cues.

Depth cues are visual information that helps our brain to accurately judge the distance of an object from the retina.

Size cues are very similar to Depth cues. However, they look for information about the size of an object.

What is Relative Size Psychology?

Relative size is a perceptual cue that allows you to determine how close objects are to an object of known size.

However, sometimes our perceptions are faulty and very easy to trick into incorrectly estimating the size of objects.

For example, human meat bags (such as you and I) use relative size to judge the size of the moon.

When the moon is close to the horizon our brain thinks that it is far larger than what it actually is.

Similarly, when the moon is high in the sky and despite its mass and distance not changing, our brain is tricked into thinking that it is far smaller than what it is.

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Therefore, what we perceive to be the size and distance of objects around us, is actually a simulation that our brain constructs in real-time.

How Does Relative Size Work?

When you see an object, your brain compares it to other objects in your field of view.

If the object is nearby, your brain assumes that it is bigger than if it were far away.

This occurs because our brains are trying to make sense of the world around us.

As previously mentioned, the way that our brain estimates the size of the moon depends on how close it is to the horizon.

When the moon is near the horizon, it is surrounded by objects that are much closer to us than when it is high in the sky.

This makes the moon appear bigger than it actually is because the objects in our field of view are comparatively large when compared to ourselves.

For example an ocean, a tree or a house.

Why Does Relative Size Matter?

Relative size plays an important role in our everyday lives and is particularly useful when driving, walking, or taking part in any activity which requires distance judgments.

Humans also use relative size to determine whether objects are bigger than others,

If the object is near other objects that are closer to you, your brain will assume that it is bigger than if it were far away.

This phenomenon is called the Ebbinghaus illusion and it is the result of the human brain mistakenly thinking that objects placed further away from us are smaller than objects that are closer to us.

This happens because when we see something far away, our brains have more time to compare it to other objects in the distance, which makes it look smaller.

When something is close to us, our brains don’t have less time and information to make those comparisons, so it looks bigger.

You would compare the size of the car in your field of view with the size of the car next to you.

If the car next to you is bigger, then you would know that it is not safe to make the turn.

Relative size can also be helpful when judging the distance between two objects.

If you are trying to pick up a pen from the ground, your brain would use relative size to estimate how close or far away the pen is.

What Does Relative Size Psychology and Size Constancy Psychology Have to do with Pricing Psychology?

Pricing Psychology
Pricing Psychology works in a very similar way.

Pricing psychology is a fascinating topic for anyone with an interest in conversion rate optimization, but more importantly, it’s something that’s often overlooked when it comes to website design.

Research has shown that our brains also confuse numerical size.

Taking an e-commerce page as an example, if you see a price in a large font, your subconscious automatically assumes that the price is high, regardless of the numerical value.

Here is what I mean:

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Was: $39.99

Now: $99.99

There is a significant difference in both prices, but unless you are paying close attention, then your brain will subconsciously estimate both values based on the size of the font.

Therefore, you may have thought that the price of $99.99 was a smaller sum than $39.99.

This is a neat trick to use when framing the price of your products and services on your webpage.

It’s also ideal for displaying discounts when you use the amount saved in a larger font than the total price.

This is because visitors to your product page will think that the amount they save is far larger than the monetary value that they will have to pay.

Price Endings and Pricing Psychology

What is a “price ending?” Price endings are the very last digit of a sum after the currency symbol.

If your digital camera was listed at $499, then the price ending would be “9.”

Oddly, price endings have a significant impact on how people perceive prices.

In 2005, researchers for Coulter & Coulter found that when prices ended in 9, people perceived the product to be 28% cheaper than those with a price ending of 0!

Reference Prices and Pricing Psychology

What is a “reference price?”

A reference price is a sum that we use to judge the value of a product.

For example, if you are considering buying a new TV, your reference price might be the price of your old TV.

Ariely (Coulter & Coulter, 2005) found that when a product had a higher reference price, people were more likely to buy it.

In one study, Ariely (Coulter & Coulter, 2005) found that people were willing to pay more for a product when the reference price was higher.

However, when the reference price was lower than the current price, people were less likely to buy the product.

Haan et al. (2011) looked at how the use of discounts can impact customer behaviour.

They found that when discounts were framed as being a “percentage off,” customers were more likely to buy the product.

However, when discounts were framed as being a monetary amount off, customers were less likely to buy the product.


Used strategically and thoughtfully, price psychology can generate more sales, increase customer price satisfaction, and boost conversion rates by incorporating Relative Size Psychology and Size Constancy Psychology.

However, this subtle manipulation of the price won’t fool everyone into thinking that what you’re offering is an unmissable deal – in particular, your selling something that nobody needs.

Thanks for reading The Powerful Relationship Between Size Constancy Psychology, Relative Size Psychology & Pricing Psychology.


Ariely, D. (2005). Behavioural economics: It’s time to change how we think about money. Harvard Business Review, 83(9), 16.

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