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Pack-Size Elasticity Calculator

Build the RSP/kg Incentive Curve for a 4-pack portfolio, get the Upsize pack under the Routine anchor per kilo and into the guidance range of roughly 70 to 85, and verify the 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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Guided walkthrough

Explore the tool, from setup to common mistakes

Five short sections explain the scenario, what each control does, how to read the output, and the mistakes to avoid. Open whichever helps. The tool above works without them.

5.1Scenario setup

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

You are the PPA Lead on a premium biscuits portfolio heading into the annual category review with a top‑3 grocery retailer. The category manager has flagged that your 28‑piece biscuit pack has been trailing volume expectations. Shoppers keep picking the 15‑piece routine size, and at the current $6.59 the 28‑piece gives them almost nothing for buying nearly twice as much: $0.235 a biscuit against $0.246, about 4 percent. Your Consumer Insight team ran a small pack‑preference study and the diagnosis is clear. Per kilo the 28‑piece is $11.77 against the 15‑piece's $8.79, so it is 34 percent DEARER, and shoppers correctly work out that sizing up costs them more. The promise a bigger pack makes is broken.

You have until Friday, and there are three things to land. You need to build the corrected RSP/kg incentive curve. You need to pick an Upsize shelf price you can defend in the room, and the rule there is that it has to cost less per kilo than the Routine, with guidance putting it around index 70 to 85, which is enough of a per‑kilo saving for a shopper to feel without handing away more margin than the extra volume can earn back. And you need to check the Golden Rule still holds, meaning no larger pack is priced below a smaller one on the shelf tag.

Your objective

Use the calculator to diagnose the broken Incentive Curve, pick an Upsize price that gets the pack under the Routine per kilo and into the guidance range of roughly 70 to 85, and verify the 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 its RSP/kg divided by the Routine's RSP/kg, times 100. Moving the Routine slider re‑anchors the ENTIRE curve. Lift the Routine price 5 percent and every other pack's index drops about 4.8 percent without a single one of them physically moving. That is why Routine pricing is the most consequential slider on the page.

  • One rule and one range. The rule: the Upsize RSP/kg must sit below the Routine's, or the promise a bigger pack makes fails, and at index 100 or above it is already broken. The range is guidance: practitioners work an Upsize pack to roughly index 70 to 85, a 15 to 30 percent per‑kilo saving. At the default Routine RSP/kg of $8.79/kg that means an Upsize RSP/kg of $6.15 to $7.47, which at 560g is a $3.44 to $4.18 shelf price. Go below 70 and the extra per‑kilo gap has to earn itself back in volume, which is a break‑even question rather than a verdict.

  • 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 portfolio has a built‑in tension. Upsize is the heaviest pack (560g) but not the most premium (Upscale at 480g, $5.49, indexes 130 on price per kilo). Because the Golden Rule sorts by weight, the Upsize's absolute price must sit above Upscale's, so at Upscale $5.49 the Upsize minimum is just above $5.49. At 560g, a $5.50 Upsize gives an RSP/kg of $9.82 and an index of 112, which still reads as no incentive. Landing Upsize in the 70 to 85 band at this portfolio means either dropping Upscale's price, which destroys its premium positioning, or re‑designing the ladder so Upscale is not lighter than Upsize.

  • The pack portfolio shape is fixed here. You can change prices and nothing else. In a real portfolio decision the Incentive Curve is the SECOND step; the FIRST is deciding which pack weights to offer at all (Pack Roles Framework, PPA Lesson 2). This tool tells you when the shape of the portfolio is what is fighting you.

5.2Controls & toggles

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

ControlRangeDefaultWhat it changes
Entry (10-piece) price slider$1.80 to $3.60 in $0.01 steps$2.70 (280g · RSP/kg $9.64 · index 110)Shelf price of the accessible-entry-point pack. Guidance for an Entry pack is roughly index 110 to 130, because small formats cost more per unit to make and that premium funds a low price on the shelf. Sitting above the Routine per kilo is the design working here. Weight 280g.
Routine (15-piece) price slider$2.50 to $5.00 in $0.01 steps$3.69 (420g · anchor · index 100 by definition)The anchor pack, always at index 100 by construction. Moving it re-shapes every other pack's index: lift it 5 percent and the others drop about 4.8 percent each. The most consequential single slider on the page.
Upsize (28-piece) price slider$3.20 to $7.50 in $0.01 steps (hard floor and ceiling)$6.59 (560g · RSP/kg $11.77 · index 134 · BROKEN)The trade-up pack. It must cost less per kilo than the Routine, which is the rule; guidance puts it around index 70 to 85, which here is a shelf price of $3.44 to $4.18. Note that the slider will happily let you drag it below Upscale's price. The Golden Rule is enforced by the red warning panel after the fact rather than by blocking the drag. At the default Upscale of $5.49, the cheapest Upsize that keeps the rule is $5.50, and anything below that fires a violation warning.
Upscale (12-piece premium) price slider$3.80 to $7.00 in $0.01 steps$5.49 (480g · RSP/kg $11.44 · index 130)Premium pack. Guidance is index 120 and above, because a premium format earns more per kilo by design and is not on the value ladder at all. It is lighter than Upsize (480g against 560g), so in the weight ordering the Golden Rule uses it sits below Upsize, and its price has to stay below the Upsize price.
The promise panelrule kept / rule broken, plus a distance from guidancerule broken at the default prices (Upsize index 134)One of the page's two absolutes, and the one about price per kilo. It goes red the moment the Upsize costs more per kilo than the Routine, because at that point the bigger pack is the worse deal in every category. The Golden Rule panel is the other. Below index 100 this one reports how far the pack sits from the guidance for its role, and it never calls a price wrong for sitting outside a range no study sets.
Golden Rule panelOK / ViolationOK at the default prices ($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 means arbitrage risk: shoppers buy the larger pack because it costs less 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 promise panel and the pack‑ladder diagnostic table.

    Expected outcome: Upsize (28-piece) at $6.59 gives an RSP/kg of $11.77 and an index of 134, so the rule is broken: the Upsize costs MORE per kilo than the Routine. Routine RSP/kg is $8.79. The Golden Rule reads OK, because prices ascend with weight ($2.70 < $3.69 < $5.49 < $6.59). The ladder table reads Entry on guidance, Routine the anchor, Upsize outside guidance, Upscale on guidance. 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 percentage margin off factory cost rather than by targeting RSP/kg indices.
  2. Push the Upsize into its guidance range, 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 x 100 = 81.3, inside the guidance range. But the Golden Rule now fires a violation: the 28-piece Upsize at $4.00 sits below the 12-piece Upscale premium at $5.49, and because Upsize is the heavier pack at 560g the rule requires its price to be above the lighter Upscale's. The tool shows you both findings at once. This is the built-in 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: The Golden Rule recovers: by weight, $2.70 Entry < $3.69 Routine < $3.99 Upscale < $4.00 Upsize. Upsize index is still 81, inside guidance. But Upscale RSP/kg = 3.99 / 0.480 = $8.31/kg gives an index of 94.6, far under its 120-and-above marker, so the Upscale now sits below the Routine per kilo: a premium format priced like a value one. The trade-off is now visible. You solved the Upsize trade-up problem by destroying the Upscale premium positioning.
  4. See the ceiling this pack portfolio runs into, where both targets cannot hold

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

    Expected outcome: You will find there is NO price set at which all four conditions hold at once: (a) Upsize inside 70 to 85, (b) Upscale at 120 or above for its premium position, (c) Golden Rule OK, meaning Upsize above Upscale on the price tag, (d) Entry at 110 or above. The weights are what block it. Upsize weighs 560g and is the heaviest, Upscale weighs 480g, so the Upsize absolute price must sit above the Upscale price. To hit an Upsize index of 70 to 85, Upsize RSP/kg has to be 85 percent of the Routine's $8.79 or less, which is $7.47/kg, and at 560g that caps the Upsize price at $4.18. But then Upscale must come in at $4.18 or below too, and at 480g that is an RSP/kg of $8.71, under the Routine's $8.79, which puts Upscale below index 100 and stops it being premium at all. Some pack portfolio shapes make the Incentive Curve unsolvable until you re-design the ladder itself.
  5. Re-anchor the curve, the most underrated lever

    Reset. Raise the Routine 15‑piece from $3.69 to $4.50, a lift of 22 percent.

    Expected outcome: New Routine RSP/kg = 4.50 / 0.420 = $10.71/kg. Every OTHER pack's index re-shapes on its own: Entry index 9.64 / 10.71 x 100 = 90, down from 110, and now under the Routine, which invites a trade DOWN. Upsize index 11.77 / 10.71 x 100 = 110, still above the Routine, so the rule is still broken. Upscale index 11.44 / 10.71 x 100 = 107, down from 130 and now well under its 120 marker. The whole ladder moved without any other price physically changing. Routine pricing is the fulcrum, so a review that only looks at the Upsize price and leaves the Routine alone has missed the highest-leverage move available. Push the Routine lift too far, though, and it demotes the Upsize and the Upscale together.
  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, below the guidance range and a deep per-kilo gap to earn back. And the Golden Rule fires a hard violation. The panel walks the ladder in weight order and stops at the first pair that breaks, which here is the 480g premium pack sitting directly under the 560g Upsize: "28-piece at $3.20 is below 12-piece premium at $5.49. The larger pack unit price must not drop below the next smaller pack." That the premium pack is the one it catches first is the whole built-in tension of this portfolio in one line. Now picture the shopper. Everyone who was buying the 15-piece at $3.69 switches to the 28-piece at $3.20, walking out with MORE biscuits for LESS MONEY. The Routine collapses, and the ladder goes with it. The Golden Rule is ABSOLUTE. Violate it and no amount of Incentive Curve optimization 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: The point to take away is that when a pack portfolio leaves the Incentive Curve with no price that works (Step 4), the fix belongs in pack design rather than in pricing. Either make Upscale the premium-PRICED lightest pack in the ladder, say a 200g artisanal version at $4.99, which is $25/kg and an index of 284, so clearly premium. Or drop Upscale entirely and put a variety multi-pack in its place, which does not compete on price per kilo at all. The Incentive Curve is the DIAGNOSTIC tool and Pack Roles is the CORRECTIVE one. Open the PPA Lesson 2 Pack Roles concept page for the four pack roles (Entry, Routine, Upsize, Upscale) and the guidance that keeps a ladder out of this 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 divided by (weight in grams divided by 1000)The per-kilo shelf cost of each pack, and the single most important number in the pack ladder. It is what shoppers instinctively compare when they choose between sizes, even when they never consciously work the numbers out.
Index (per pack)(pack RSP/kg divided by Routine RSP/kg) x 100Every pack's position on a normalized scale where Routine = 100. Guidance: Entry roughly 110 to 130, Routine 100 by definition, Upsize roughly 70 to 85, Upscale 120 and above. These are practitioner starting points rather than researched constants. An index is a relative signal, so changing the Routine price re-shapes every other index.
The promise a bigger pack makesUpsize RSP/kg against Routine RSP/kgOne of the two absolute readings here, alongside the Golden Rule on shelf price. At index 100 or above the bigger pack costs more per kilo than the everyday one, so the promise fails, in every category. Below that the tool reports how far the pack sits from the guidance for its role. A ladder inside guidance is where the Triple Win lives: the shopper pays less per kilo, the retailer's category grows in value, and the maker earns longer production runs.
Golden Rulesort the packs by weight, then check that each pack's price is at least the price of the pack below itAbsolute shelf price must ascend with pack weight. A violation creates shopper arbitrage, where they buy the larger pack because it costs less on the tag. This one is non-negotiable, and every other finding is moot while it is firing.
Ladder reading (per row)role-specific reading against that role's own guidancePer pack: 'Anchor' for the Routine, then 'On guidance', 'Near guidance', or the guidance range the pack currently sits outside. It reports a distance rather than a verdict, because the markers are starting points and a pack a few points out is inside the noise.

Read the Golden Rule panel FIRST, because if it fires, every other reading is moot and the violation is what you fix. Then read the promise panel, which is the single most important outcome of the whole analysis. The pack ladder diagnostic table is the per‑pack detail you will want for the defence in the category review. When the tool shows a built‑in tension, where the Golden Rule holds and the Upsize still cannot reach the 70 to 85 band, the fix has moved out of this tool and into pack‑portfolio redesign (see PPA Lesson 2 Pack Roles).

5.55 common mistakes to avoid

Diagnostic patterns that catch the most common misuse of this calculator.

  1. Mistake 1Optimizing the Upsize price in isolation without checking Golden Rule
    Symptom: Upsize lands inside the 70 to 85 guidance range, but a red Golden Rule warning fires. The price cut pushed Upsize below Upscale on absolute price.
    Fix: The Golden Rule is ABSOLUTE. Violate it and shoppers arbitrage instantly. Where the Upsize price can land is constrained by the next-heaviest pack's absolute price as much as by its own index target. If Upscale is $5.49 and the weights are 480g for Upscale against 560g for Upsize, the minimum Upsize price is just above Upscale at $5.50. Any move below that breaks the ladder, however 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 to 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. Lifting the Routine price 5 percent drops every other pack's index by about 4.8 percent, the same effect as a targeted Upsize cut, and it never touches the Upsize price. Before you decide the pack portfolio is broken, try raising the Routine by 10 to 20 percent. That is often the cleanest fix, because it protects Upsize margin and shifts the whole curve toward healthier indices at the same time.
  3. Mistake 3Assuming Upsize is the heaviest pack in every portfolio
    Symptom: Applying the 70 to 85 Upsize guidance to a pack that is actually an Upscale, with premium positioning at a LIGHTER weight than Upsize, leads to the wrong price recommendation.
    Fix: In PPA taxonomy, Upsize is the biggest-volume-per-dollar pack, at maximum weight with a discount per kilo. Upscale is the most-premium-per-dollar pack, often a lighter pack with premium ingredients, format or branding. They are DIFFERENT roles read against DIFFERENT markers. Guidance for an Upsize is roughly 70 to 85; for an Upscale it is 120 and above, because a premium format earns more per kilo by design. Always verify which role a given SKU is playing BEFORE reading it against a marker. A pack sold as 'premium size' might be an Upscale-role pack that should never drop per-kilo below the Routine at all.
  4. Mistake 4Ignoring the built-in tension when the default pack portfolio can't solve both targets at once
    Symptom: Hours spent moving sliders find no price set that satisfies Upsize inside 70 to 85, Upscale at 120 or above, the Golden Rule holding, and Entry at 110 or above. Conclusion: "the model is broken."
    Fix: The model is doing its job. What is broken is the pack portfolio. Some weight configurations, where the heaviest pack is the Upsize and the second-heaviest is a premium Upscale, cannot satisfy all four indices at once, because the per-kilo maths forces a trade-off. The fix is pack-portfolio redesign: make Upscale the lightest premium pack, say a 200g artisanal SKU, so it drops out of the weight-ordered Golden Rule comparison. The RSP/kg Incentive Curve tool shows you 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, something like -0.8, and getting an index of 134 instead.
    Fix: True pack-size elasticity, meaning how volume responds to a change in pack weight while price is held constant, needs a scanner-data regression, and this tool does not produce it. What it does produce is the RSP/kg Incentive Curve, which is how pack-size elasticity shows up operationally, as a price signal running across the packs. A shopper never sees an elasticity coefficient. They see the price per kilo, and the Incentive Curve index is what puts a number on that signal. For the 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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