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Pack-Size Elasticity Calculator

Build the RSP/kg Incentive Curve for a 4-pack portfolio, land the Upsize pack in the 70-85 trade-up band versus the Routine anchor, and verify the PPPA Golden Rule holds before committing a pack-ladder price review. The same interactive model the full RGM Academy course uses for PPA Lesson 3 — no auth, no paywall.

Updated 23 April 2026Extracted from the Price Pack Architecture module, lesson 3: RSP/kg Incentive Curve
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Scenario walkthrough

Tap any section to explore in detail

5.1Scenario setup

The starting SKU, market, and assumptions the model makes.

You are the PPA Lead on a frozen foods portfolio heading into the annual category review with a top-3 grocery retailer. The category manager has flagged that your 28-piece fish-fingers pack has been trailing volume expectations — shoppers keep picking the 15-piece routine size even though the 28-piece would give them a 24% per-pack discount at the current $6.59 price. Your Consumer Insight team ran a small pack-preference study and the diagnosis is clear: the 28-piece's RSP per kg is HIGHER than the 15-piece — shoppers correctly identify that sizing up actually costs them more per kg than their current pack. The Incentive Curve is broken.

Your job by Friday: build the corrected RSP/kg incentive curve, pick a defensible Upsize shelf price that lands in the 70-85 index target band (enough price-per-kg discount to motivate trade-up, not so much that you give margin away), and verify the PPPA Golden Rule holds — no larger pack priced below a smaller pack on absolute shelf price.

Your objective

Use the calculator to diagnose the broken Incentive Curve, pick an Upsize price that lands in the 70-85 target trade-up band, and verify the PPPA Golden Rule holds across all four packs.

Key assumptions

  • The Routine pack is the ANCHOR at index 100 by definition. Every other pack's index is computed as (Pack RSP/kg ÷ Routine RSP/kg) × 100. Moving the Routine slider re-anchors the ENTIRE curve — a +5% Routine price lift causes a −4.8% drop in every other pack's index without them physically moving. This is why Routine pricing is the most consequential slider on the page.

  • Target Upsize band is index 70-85 — meaning the Upsize RSP/kg must be 15-30% BELOW the Routine's. At the default Routine RSP/kg of $8.79/kg, the Upsize target RSP/kg is $6.15-$7.47, which at 560g translates to a $3.44-$4.18 shelf price. Below 70 = margin give-away; 86-100 = weak trade-up; 100+ = no incentive; 120+ = inverted/broken curve.

  • PPPA Golden Rule: absolute shelf price must ascend with pack weight. Sort the ladder by weight (Entry 280g / Routine 420g / Upscale 480g / Upsize 560g) and verify prices are non-decreasing. An Upsize that is heavier than Upscale but priced below Upscale would create an arbitrage — shoppers buy the larger pack because it's cheaper, and the whole ladder collapses.

  • The default pack architecture has a structural tension: Upsize is the HEAVIEST pack (560g) but not the MOST PREMIUM (Upscale at 480g, $5.49, indexes 130 on price-per-kg). Because Golden Rule sorts by weight, the Upsize's absolute price must sit ABOVE Upscale's absolute price. At Upscale $5.49, the Upsize MINIMUM price per Golden Rule is just above $5.49. At 560g, $5.50 Upsize RSP/kg = $9.82 → index 112 (still 'no-incentive'). Landing Upsize in the 70-85 band at this portfolio configuration requires EITHER dropping Upscale's price (destroying its premium positioning) OR re-architecting the ladder so Upscale is not heavier than Upsize.

  • The pack portfolio shape is fixed in this sandbox — you cannot change weights, only prices. For a real portfolio decision, the Incentive Curve analysis is the SECOND step; the FIRST step is deciding which pack weights to offer (Pack Roles Framework, PPA Lesson 2). This tool flags when the portfolio shape itself is fighting the Incentive Curve math.

5.2Controls & toggles

Every input the calculator exposes, its range, and what it changes.

ControlRangeDefaultWhat it changes
Entry (10-piece) price slider$1.80 – $3.60 in $0.01 steps$2.70 (280g · RSP/kg $9.64 · index 110)Shelf price of the accessible-entry-point pack. Entry indices ≥105 = 'Accessible'; <105 = 'Too cheap' (cannibalises Routine). Weight 280g.
Routine (15-piece) price slider$2.50 – $5.00 in $0.01 steps$3.69 (420g · anchor · index 100 by definition)The anchor pack. Always index 100 by construction. Moving this re-shapes every other pack's index — a +5% Routine move = every other index drops ~4.8%. The most consequential single slider.
Upsize (28-piece) price slider$3.20 – $7.50 in $0.01 steps (hard floor and ceiling)$6.59 (560g · RSP/kg $11.77 · index 134 · BROKEN)The trade-up pack. Target index 70-85 = shelf price $3.44-$4.18. Note: the slider does NOT prevent dragging below Upscale's price — the PPPA Golden Rule is enforced by the red warning panel AFTER the fact, not by blocking the drag. At default Upscale $5.49, the Golden-Rule-compliant minimum Upsize is $5.50, below which the panel fires a violation warning.
Upscale (12-piece premium) price slider$3.80 – $7.00 in $0.01 steps$5.49 (480g · RSP/kg $11.44 · index 130)Premium pack. Indices ≥110 = 'Premium'; <110 = 'Underpriced'. Lighter than Upsize (480g vs 560g), so on Golden Rule ordering it sits BELOW Upsize — its price must sit below Upsize's price.
Upsize Trade-Up Zone indicator6 bands"Broken (Inverted)" at seed (index 134)Classifies Upsize index: Optimal (70-85), Weak (86-99), No Incentive (100-119), Broken (≥120), Over-Discounted (60-69), Margin Destruction (<60). The target is Optimal.
PPPA Golden Rule panelOK / ViolationOK at seed ($2.70 < $3.69 < $5.49 < $6.59 by weight)Sorts packs by weight (280g / 420g / 480g / 560g) and verifies absolute prices are non-decreasing. A violation indicates arbitrage risk — shoppers buy the larger pack because it's cheaper on the tag.
5.3Step-by-step exploration

7-step guided exploration of the scenario.

  1. Read the default broken curve — where most real portfolios start

    Leave every control at default. Read the Upsize Trade-Up Zone indicator and the pack-ladder diagnostic table.

    Expected outcome: Upsize (28-piece) at $6.59 → RSP/kg $11.77 → index 134 → "Broken (Inverted)" (the Upsize is actually MORE expensive per kg than the Routine). Routine RSP/kg $8.79. PPPA Golden Rule OK (prices ascend with weight: $2.70 < $3.69 < $5.49 < $6.59). Ladder diagnostic table shows: Entry 'Accessible', Routine 'Anchor', Upsize 'Broken', Upscale 'Premium'. This is the real-world starting position — a lot of FMCG pack ladders have exactly this shape because Upsize SKUs get priced by taking a fixed % margin off factory cost rather than by targeting RSP/kg indices.
  2. Push the Upsize into the optimal band — the intended trade-up fix

    Drag the Upsize slider from $6.59 down to $4.00.

    Expected outcome: New Upsize RSP/kg = 4.00/0.560 = $7.14/kg. Index = 7.14/8.79 × 100 = 81.3 → "Optimal Trade-Up Window" (green band). BUT the PPPA Golden Rule now FIRES a violation: Upsize 28-piece at $4.00 is below Upscale 12-piece premium at $5.49 (Upsize is heavier at 560g, so Golden Rule requires its price to be above the lighter Upscale's price). The tool surfaces both findings simultaneously — this is the structural tension the default pack portfolio creates.
  3. Resolve the Golden Rule violation — drop Upscale to re-enable Upsize

    Keep Upsize at $4.00. Drop the Upscale 12-piece premium from $5.49 to $3.99.

    Expected outcome: Golden Rule recovers: by weight $2.70 Entry < $3.69 Routine < $3.99 Upscale < $4.00 Upsize. Upsize index still 81 (Optimal). BUT Upscale RSP/kg = 3.99/0.480 = $8.31/kg → index 94.6 → NOT premium anymore — Upscale has been demoted below Routine on price-per-kg. The 'Premium' verdict in the diagnostic table flips to 'Underpriced'. Trade-off revealed: you solved the Upsize trade-up problem at the cost of destroying the Upscale premium positioning.
  4. See the structural ceiling — this pack portfolio can't solve both

    Reset. Then try all combinations: raise Upscale, lower Upsize, any permutation where Upsize > Upscale on absolute price AND Upsize indexes 70-85.

    Expected outcome: You will find there is NO price set at which all four conditions hold simultaneously: (a) Upsize index 70-85, (b) Upscale index ≥110 for premium positioning, (c) Golden Rule OK (Upsize > Upscale absolute), (d) Entry index ≥105. The reason: Upsize weighs 560g (heaviest), Upscale weighs 480g — so Upsize absolute price must sit above Upscale. To hit Upsize index 70-85, Upsize RSP/kg must be ≤85% of Routine ($8.79) = $7.47/kg. At 560g that's Upsize price ≤$4.18. But then Upscale must be ≤$4.18 and at 480g that's RSP/kg ≤$8.71 = below Routine's $8.79 = Upscale below index 100 = NOT premium. The lesson: some pack portfolio shapes make the Incentive Curve unsolvable without first re-designing the ladder.
  5. Re-anchor the curve — the most underrated lever

    Reset. Raise the Routine 15-piece from $3.69 to $4.50 (+22%).

    Expected outcome: New Routine RSP/kg = 4.50/0.420 = $10.71/kg. Every OTHER pack's index re-shapes automatically: Entry index 9.64/10.71×100 = 90 (was 110 → now 'Too cheap' — invited to trade DOWN), Upsize index 11.77/10.71×100 = 110 (still 'No Incentive', but no longer Broken), Upscale index 11.44/10.71×100 = 107 (was 130 → falls BELOW the 110 premium threshold, verdict flips from 'Premium' to 'Underpriced'). The whole ladder moved without physically changing any other price. Implication: Routine pricing is the fulcrum — a review that only looks at Upsize price and leaves Routine alone misses the highest-leverage move, AND a Routine lift that's too large simultaneously demotes both the Upsize AND Upscale tiers.
  6. Test the Golden Rule floor — drop Upsize below Routine

    Reset. Drag the Upsize slider all the way down to its minimum $3.20.

    Expected outcome: Upsize RSP/kg = 3.20/0.560 = $5.71/kg. Index = 65 → "Over-Discounted". But the PPPA Golden Rule fires a hard violation: "28-piece at $3.20 is below 15-piece at $3.69 — the larger pack unit price must not drop below the next smaller pack." Shopper arbitrage scenario: every shopper who was buying the 15-piece at $3.69 switches to the 28-piece at $3.20, buying MORE fish fingers FOR LESS MONEY. Routine collapses. The whole ladder collapses. Golden Rule is ABSOLUTE — violate it and no amount of Incentive Curve optimisation matters.
  7. Map back to PPA Lesson 2 (Pack Roles) — where the fix actually lives

    Open the Pack Roles Framework and OBPPC Framework related-concept links below.

    Expected outcome: Understanding that when a pack portfolio makes the Incentive Curve structurally unsolvable (Step 4), the fix isn't in pricing — it's in pack design. Either (a) make Upscale the premium-PRICED lightest pack in the ladder (e.g. 200g artisanal version at $4.99 = $25/kg index 284 → clearly premium), OR (b) eliminate Upscale entirely and replace with a variety multi-pack that doesn't compete on per-kg price. The Incentive Curve is a DIAGNOSTIC tool; Pack Roles is the CORRECTIVE tool. Open the PPA Lesson 2 Pack Roles concept page to see the five canonical roles (Entry / Routine / Upsize / Upscale / Entry-premium) and the guardrails that prevent this structural dead-end.
5.4Reading the output

Every KPI, the formula behind it, and how to interpret a positive or negative value.

KPIFormulaHow to read it
RSP/kg (per pack)price ÷ (weight_g ÷ 1000)The per-kilo shelf cost of each pack. The single most important number in the pack ladder — it's what shoppers instinctively compare when choosing between sizes (even if they don't do the arithmetic consciously).
Index (per pack)(pack RSP/kg ÷ Routine RSP/kg) × 100Every pack's position on a normalised scale where Routine = 100. Target bands: Entry ≥105, Routine 100 (by definition), Upsize 70-85, Upscale ≥110. An index is a relative signal; changing the Routine price re-shapes every other index.
Upsize Trade-Up Zoneband lookup over Upsize index6 bands: Optimal (70-85), Weak (86-99), No Incentive (100-119), Broken (≥120), Over-Discounted (60-69), Margin Destruction (<60). The Optimal band is the Triple Win — shopper gets price-per-kg savings, retailer gets volume, manufacturer gets scale economies.
PPPA Golden Rule∀i: price[weight_i+1] ≥ price[weight_i] after sorting by weight ascendingAbsolute shelf price must ascend with pack weight. A violation creates shopper arbitrage — buy the larger pack because it costs less on the tag. Non-negotiable; every other finding is moot if Golden Rule fires.
Ladder Verdict (per row)role-specific classification against index targetPlain-English verdict per pack: 'Anchor' / 'Accessible' / 'Too cheap' / 'On target' / 'Weak trade-up' / 'Broken' / 'Over-discounted' / 'Premium' / 'Underpriced'. The fastest way to spot which pack is the structural problem.

Read the PPPA Golden Rule panel FIRST — if it fires, every other reading is moot (fix the violation before anything else). Then read the Upsize Trade-Up Zone — that's the single most important outcome of the whole analysis. The pack ladder diagnostic table is the per-pack detail for the defence in the category review. When the tool surfaces a structural tension (Golden Rule holding AND Upsize can't reach the 70-85 band simultaneously), the fix isn't in this tool — it's in pack-portfolio redesign (see PPA Lesson 2 Pack Roles).

5.55 common mistakes to avoid

Diagnostic patterns that catch most misuse of this calculator in practice.

  1. Mistake 1Optimising the Upsize price in isolation without checking Golden Rule
    Symptom: Upsize lands in the 70-85 optimal band, but a red Golden Rule warning fires — the price cut pushed Upsize below Upscale on absolute price.
    Fix: Golden Rule is ABSOLUTE — violate it and shoppers arbitrage instantly. The Upsize-price landing zone is CONSTRAINED by the next-heaviest pack's absolute price, not just by its own index target. If Upscale is $5.49 and weights are 480g (Upscale) < 560g (Upsize), the minimum Upsize price is just above Upscale = $5.50. Any move below that breaks the ladder regardless of how good the RSP/kg indexing looks.
  2. Mistake 2Treating Routine as a fixed anchor — not moving it during the analysis
    Symptom: Upsize can't reach the 70-85 band without breaking Golden Rule, and the conclusion is "we need to redesign the pack portfolio."
    Fix: Routine is the fulcrum of the entire curve. A +5% Routine price lift drops every other pack's index by ~4.8% — the same effect as a targeted Upsize cut, but without touching the Upsize price. Before deciding the pack portfolio is broken, try raising Routine by 10-20% first. This is often the cleanest fix because it protects Upsize margin AND shifts the whole curve toward healthier indices.
  3. Mistake 3Assuming Upsize = heaviest pack in every portfolio
    Symptom: Applying the 70-85 target band to a pack that is actually Upscale (premium positioning at a LIGHTER weight than Upsize) leads to the wrong price recommendation.
    Fix: In PPA taxonomy, Upsize = the biggest-volume-per-dollar pack (maximum weight, discount per kg); Upscale = the most-premium-per-dollar pack (often a lighter pack with premium ingredients / format / branding). They are DIFFERENT roles with DIFFERENT index targets. Upsize target 70-85; Upscale target ≥110. Always verify which role a given SKU is playing BEFORE applying index targets — a pack sold as 'premium size' might actually be an Upscale-role pack that shouldn't drop per-kg below Routine at all.
  4. Mistake 4Ignoring the structural tension when the default pack portfolio can't solve both targets simultaneously
    Symptom: Hours spent moving sliders find no price set that satisfies (Upsize index 70-85) AND (Upscale index ≥110) AND (Golden Rule holds) AND (Entry index ≥105). Conclusion: "the model is broken."
    Fix: The model isn't broken — the pack portfolio is. Some weight configurations (heaviest pack = Upsize, second-heaviest = Upscale at a premium) cannot satisfy all four indices simultaneously; the per-kg math forces a trade-off. The fix is pack-portfolio redesign: make Upscale the lightest-premium pack (e.g. a 200g artisanal SKU) so it is excluded from the weight-ordered Golden Rule. The RSP/kg Incentive Curve tool surfaces this tension; PPA Lesson 2 Pack Roles is where the fix lives.
  5. Mistake 5Confusing pack-size elasticity (Ex/%w) with the RSP/kg Incentive Curve
    Symptom: Expecting the calculator to output an elasticity coefficient (e.g. −0.8) and getting an index (134) instead.
    Fix: True pack-size elasticity (how volume responds to a pack-weight change holding price constant) requires a scanner-data regression; this tool doesn't produce it. What this tool DOES produce is the RSP/kg Incentive Curve — the operational expression of pack-size elasticity via the cross-pack price signal. Shoppers don't see elasticity; they see RSP/kg. The Incentive Curve index translates the latent pack-size elasticity into the signal shoppers actually respond to. For the elasticity coefficient itself, cross-reference the [Price Elasticity Calculator](/tools/price-elasticity-calculator) with Upsize-pack scanner data.
Related concepts

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This calculator is the sandbox slice of Lesson 3: RSP/kg Incentive Curve. Each of the other 6 Price Pack Architecture lessons teaches a complementary concept that sharpens how you read the output above.

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