The 19th-century discovery that still governs consumer pricing

Ernst Heinrich Weber, a German physiologist working in the 1830s and 1840s, ran systematic experiments on weight discrimination. His finding was counterintuitive: whether a person notices a change in stimulus depends not on the absolute amount of the change but on its ratio to the original. Add 1 gram to a 10-gram weight and it is detectable. Add 1 gram to a 100-gram weight and it is invisible. The ratio required for detection — the just noticeable difference — remains roughly constant, regardless of where on the scale the change occurs.

Gustav Fechner formalised this in 1860, establishing mathematically that subjective sensation follows a logarithmic function of physical intensity. The combined Weber-Fechner law holds that the brain functions as a relative-change detector, not an absolute-magnitude meter. Equal ratios of stimulus change produce equal magnitudes of perceived change — not equal absolute amounts.

One honest caveat before applying this to pricing: a rigorous critique from consumer research notes that Weber’s Law and Fechner’s Law apply strictly to sensory dimensions and their concepts of sensory thresholds — and price is not a sensory dimension. The framework should be understood as a powerful analogy that generates useful pricing predictions, not as a direct transfer of sensory psychology to economic decisions. The predictions it produces are empirically supported; the precise mechanism may differ from the sensory one.

Why £10 feels massive on £50 and invisible on £500

Applied to pricing, the Weber-Fechner framework predicts that perceived price change is proportional to the ratio of the change to the base price, not to the absolute amount of the change. A £10 increase on a £50 product is a 20% change — well above any plausible just noticeable difference threshold for most consumer categories. The same £10 on a £500 product is a 2% change — well below it. The absolute amount is identical. The perceived magnitude is categorically different.

Monroe’s 1971 synthesis of the pricing psychophysics literature concluded that the subjective price scale of buyers follows a logarithmic pattern, and that there is a range of acceptable prices for any given product at any given price point. The logarithmic scale finding is the direct commercial expression of the Weber-Fechner framework: consumers are systematically less sensitive to absolute price differences as the baseline price increases.

This asymmetry has an immediate strategic implication. An entrepreneur who implements a flat £10 price increase across a product line spanning £30 to £3,000 is not making a consistent pricing decision. At £30, a £10 increase is a 33% change — dramatic, likely to trigger significant consumer response. At £3,000, it is 0.3% — invisible. The Weber-Fechner framework argues that price changes should be evaluated and implemented in percentage terms relative to the base, not in absolute terms.

The just noticeable difference as a strategic tool

The JND principle applies in both directions, and this asymmetry is commercially significant. Price increases that remain below the consumer’s relative threshold are absorbed without reaction. Discounts that fail to clear the threshold do not produce the purchasing response they were designed to generate — they are real costs to the seller and invisible to the buyer. The entrepreneur offering a 3% discount on a high-ticket service is paying a genuine cost to produce a stimulus that does not register.

Marketing research applying Weber-Fechner principles to pricing has produced a rough empirical guideline: the JND for price sits around 10% in most consumer goods categories, varying with category familiarity, competitive density, and price level. A price increase below 10% is likely to go unnoticed; a discount below 10% is likely to go unperceived. Both are strategic implications that most entrepreneurs do not account for when setting price change sizes.

Shrinkflation: the JND exploited deliberately

Cadbury applied the just noticeable difference principle when it reduced the weight of its standard Dairy Milk bar from 49 grams to 45 grams while keeping the price constant at 59p. The 8% reduction stayed below the threshold at which most consumers would detect the change through either visual inspection or consumption experience. In 2022, Cadbury reduced its 200g sharing bars to 180g — a 10% reduction — again with no change in price, citing rising production costs.

The mechanism behind both moves is identical: reduce the quantity just enough to deliver a real price increase in a form the consumer cannot directly perceive. It is the Weber-Fechner relative threshold deliberately managed to deliver value reduction below the detection threshold. The strategic inverse applies with equal force: improvements in product quality, quantity, or service level that fail to clear the JND are real costs without perceived benefits. Visible improvements require exceeding the threshold.

Airline pricing and baseline anchoring

Airlines deploy the relative threshold systematically in their ancillary pricing architecture. A £200 upgrade on a £1,500 transatlantic ticket is 13% of the base price — detectable but within the tolerance zone for many economy travellers. The same £200 for a hotel upgrade from £150 to £350 is a 133% premium that produces significant resistance. The absolute amount is identical; the baseline that governs the relative calculation is entirely different.

Airlines deliberately sequence their pricing to establish a high baseline before presenting incremental costs — bags, seats, meals, upgrades — exploiting the relative threshold to make each addition feel smaller than it would priced in isolation.

The practical formulation

Three specific applications for entrepreneurs. First, evaluate all price changes in percentage terms, not absolute ones — and know the approximate JND for your category before deciding how to structure an increase. Second, implement price increases that stay below the JND threshold incrementally over time rather than in large infrequent jumps that clear the threshold dramatically. Third, size discounts to exceed the JND — a discount that does not register is a discount that does not convert, and most of its cost is wasted.

If pricing decisions or financial pressures are significantly affecting your wellbeing or confidence, that is worth acknowledging. UK: Samaritans (116 123, free, 24/7). Mind (0300 123 3393). International: iasp.info/resources/Crisis_Centres.

A book worth reading alongside this

Pricing: Making Profitable Decisions by Kent Monroe is the most rigorous applied treatment of the Weber-Fechner framework in pricing available. Monroe’s synthesis of the psychophysics literature and its pricing applications — including his foundational 1971 work on logarithmic price scales and acceptable price ranges — is the academic text that translated the 19th-century sensory research into something directly applicable to how entrepreneurs should think about price sensitivity, change thresholds, and the relative perception of discounts and increases. For any entrepreneur who wants to understand the perceptual mechanics of pricing rather than just its economics, it is the most direct available starting point.

Have questions about this article?

If any part of this article raised questions you want to explore further, courbot.co is built for exactly that. It is courben.co’s AI assistant, designed around the psychology of entrepreneurship. Ask it anything from this article.

If pricing pressures are significantly affecting your wellbeing, speaking with a psychologist is the right next step. UK: Samaritans (116 123, free, 24/7). Mind (0300 123 3393). BACP therapist finder: bacp.co.uk/search/Therapists. International: iasp.info/resources/Crisis_Centres. Crisis Text Line — text HOME to 741741.

This article is for educational and informational purposes only. Sources: Weber, E.H. (1834/1851), foundational JND research. Fechner, G.T. (1860), Elemente der Psychophysik. Monroe, K.B. (1971), Journal of Marketing Research. Wikipedia, Shrinkflation.