Persuasion & consumer psychology · law 063
Weber–Fechner Law
Also known as: Weber's law · Just-noticeable difference
By Shivam Bhandari · Reviewed 31 October 2026 · How we write
what it means
People notice changes relative to the starting amount, not in absolute terms — a ₹50 change matters on ₹200 but not on ₹20,000.
How Weber–Fechner Law works
Perception is proportional. Customers barely notice small price changes on large purchases but react strongly to the same rupee change on small ones.
This explains why small, gradual price increases often go unnoticed, why add-ons sell well at checkout for big purchases, and why discounts must be large enough to be felt.
where it comes from
German physiologist Ernst Heinrich Weber found in 1834 that the smallest noticeable change in weight was a constant fraction of the original. Gustav Fechner extended it in 1860.
Weber–Fechner Law examples in business
Add-ons
A ₹999 extended warranty feels small next to a ₹60,000 laptop.
Price changes
A brand raises a ₹500 product to ₹520 with little reaction, but customers notice a ₹10 to ₹30 change instantly.
Discounts
A 5% discount may not be noticed; 20% usually is.
How to apply it
- 1Offer add-ons and upgrades alongside large purchases.
- 2Make discounts big enough to cross the ‘noticeable’ threshold.
- 3Keep price increases on low-priced items gentle and well-explained.
- 4Express savings as percentages or rupees, whichever looks larger.
common misreading
Using it to hide quality cuts (‘shrinkflation’) erodes trust when customers notice.
ask yourself
Are your discounts large enough for customers to actually notice?
put it into practice
Frequently asked questions
What is Weber–Fechner Law?
People notice changes relative to the starting amount, not in absolute terms — a ₹50 change matters on ₹200 but not on ₹20,000. Perception is proportional. Customers barely notice small price changes on large purchases but react strongly to the same rupee change on small ones.
Who came up with Weber–Fechner Law?
German physiologist Ernst Heinrich Weber found in 1834 that the smallest noticeable change in weight was a constant fraction of the original. Gustav Fechner extended it in 1860.
How do you apply Weber–Fechner Law in business?
1. Offer add-ons and upgrades alongside large purchases. 2. Make discounts big enough to cross the ‘noticeable’ threshold. 3. Keep price increases on low-priced items gentle and well-explained. 4. Express savings as percentages or rupees, whichever looks larger.
What is a common misunderstanding of Weber–Fechner Law?
Using it to hide quality cuts (‘shrinkflation’) erodes trust when customers notice.