A small order disappears into your medium box, while a slow-moving carton occupies valuable station space. Adding another size would improve one fit problem. Removing a size would simplify replenishment. Which change is worth making?
Carry a size when the orders it serves justify its full incremental cost, or when it provides a necessary protection capability that other packages cannot replace. That requires comparing complete assortments against the same order mix. Counting catalogue entries or chasing the tightest fit for one product will not tell you whether the operation becomes cheaper or easier to run.
Start with packable orders, not average products
An average length, width and height can describe a box that serves surprisingly few orders. Averaging separately also loses the relationships between dimensions: a long, narrow item and a short, broad bundle do not become interchangeable because their volumes are similar.
Build the demand profile from order lines and quantities. A product shipped alone, as a pair, or alongside a dissimilar item creates different packing problems. Define a packing envelope for each recurring combination: the minimum internal space needed for a permitted arrangement, including protection, separators and working clearance. Preserve alternative layouts when they are genuinely packable, rather than assuming the current arrangement is the only possibility.
The distinction matters when choosing analytical tools. Gurumoorthy and Hinge’s 2022 box-size selection study explicitly addresses single-item shipments and weights products by shipment frequency. Its results should not be treated as a ready-made solution for mixed orders. For identical rectangular inner cartons, Case Builder can screen a candidate arrangement and spacing. It does not solve mixed-order cartonization or automatically select the best box catalogue.
Protection must remain part of the fit definition. UPS’s packaging guidance distinguishes cushioning and void-fill materials by their application. Enough space for the products does not establish adequate restraint or protection. Record permissible orientations, unsupported spans, stacking restrictions and gross shipment limits alongside dimensions.
Compare two assortments against the same demand
The following scenario is entirely hypothetical, including demand, dimensions, prices and operating costs. It represents 1,000 monthly orders, each shipped in one package. The smaller assortment contains S, M and L; the expanded assortment adds compact box P and flat box F. Both retain dedicated package X, so the total number of purchased carton designs is four versus six.
Dimensions below are usable internal dimensions, not nominal outside measurements. The required envelopes already include protective space and working allowances. Only quarter-turn rotation on the base is permitted; height remains fixed during packing. That assembly rule does not guarantee upright transport; the package still needs protection for its actual distribution conditions. Equivalent protection and adequate gross-weight capacity are assumptions for every assigned pack, not test results.
| Carton | Usable inside L × W × H, mm | Landed price, USD | Availability in comparison |
|---|---|---|---|
| S | 250 × 200 × 150 | $0.70 | Both assortments |
| M | 400 × 300 × 200 | $1.05 | Both assortments |
| L | 500 × 400 × 300 | $1.65 | Both assortments |
| P | 200 × 150 × 100 | $0.55 | Expanded only |
| F | 360 × 260 × 120 | $0.82 | Expanded only |
| X | 650 × 150 × 150 | $2.50 | Dedicated, both |
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Each order family has one defined arrangement in this example. Assignments preserve that arrangement and its protection requirements; products are not compressed or rearranged to force a fit.
| Order family | Orders/month | Required envelope L × W × H, mm | Smaller → expanded carton |
|---|---|---|---|
| A: small single item | 350 | 180 × 130 × 70 | S → P |
| B: two-item bundle | 300 | 250 × 180 × 120 | S → S |
| C: flat three-item bundle | 100 | 340 × 240 × 90 | M → F |
| D: tall mixed order | 150 | 360 × 260 × 180 | M → M |
| E: bulky mixed order | 60 | 460 × 340 × 260 | L → L |
| X: fragile elongated item | 40 | 620 × 120 × 120 | X → X |
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The order-weighted mean envelope is 278.4 × 187.7 × 116.9 mm. A carton with exactly those internal dimensions accommodates only family A, or 35% of orders, under the stated rules. Even B needs more height. An average is a poor acceptance criterion.
Stock-box coverage equals orders with at least one acceptable stock-box assignment divided by all orders. Both assortments cover 960 ÷ 1,000 = 96%; including the dedicated package gives 100% planned coverage. The additional sizes improve fit for existing orders, rather than eliminate exceptions.
Family X illustrates why volume cannot substitute for fit. Its envelope occupies 8.928 liters, much less than L’s 60-liter capacity, but its 620 mm length exceeds every regular box dimension. Its end-support arrangement prohibits diagonal packing. Retain the dedicated package or route a changed configuration for manual review instead of forcing it into the general assortment.
Put the operating costs on one monthly basis
Assume fully burdened packing labor costs $36/hour, or $0.01/second. For A, moving from S to P reduces void-fill spending from $0.24 to $0.08 and packing time from 45 to 35 seconds. For C, moving from M to F changes those inputs from $0.36 to $0.12 and from 65 to 45 seconds. B, D and E each use $0.25 of void fill and 60 seconds in either assortment. X uses $0.90 of supports and fill plus 150 seconds. Existing inner packaging is unchanged; these allowances cover additional supports and fill in the shipping carton. Tape and labels add $0.10 to every order.
Packing time includes selecting, erecting, filling, closing and labeling the carton. Replenishment is separate work. Assume both assortments fit the available rack and station layout without equipment changes. Assume each regular size incurs $75/month in incremental storage, inventory control and replenishment costs; X incurs $40 in either policy. These are assumed avoidable costs, not an allocation of rent that remains unchanged. Do not add another generic labor penalty for tasks already timed.
For transport, assume an all-in contracted charge of $7 per regular order and $10 per X order, unchanged across these particular pack options. These are invented charges, not a carrier tariff. No damage-cost difference is assumed; unchanged product costs and one-time qualification or rollout costs are outside this operating comparison.
| Monthly cost, USD | Three regular sizes + X | Five regular sizes + X |
|---|---|---|
| Cartons | $916.50 | $841.00 |
| Void fill and supports | $283.50 | $203.50 |
| Tape and labels | $100.00 | $100.00 |
| Packing labor | $588.50 | $533.50 |
| Storage, control and replenishment | $265.00 | $415.00 |
| Contracted transport | $7,120.00 | $7,120.00 |
| Modeled operating total | $9,273.50 | $9,213.00 |
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For example, smaller-assortment carton spending is 650 × $0.70 + 250 × $1.05 + 60 × $1.65 + 40 × $2.50 = $916.50. Packing consumes 58,850 versus 53,350 seconds. The expanded set saves $210.50 in materials and packing, then spends $150 more on stockholding and replenishment, leaving $60.50/month before rollout costs.
There is no charge assigned to unused geometric volume. Void-fill costs come from specified material consumption, while transport follows the declared contract. In a real comparison, rerate sealed parcels using outside measurements and gross weight, including packaging tare, rather than product dimensions and net product mass. UPS’s measurement guidance illustrates the separate measurement and billing steps; the DIM guide explains that foundation. The wider delivered-cost framework is useful when damage, throughput or other costs also change.
Make each additional size earn its place
The expanded set wins overall, but that does not justify both additions. P saves $0.41 on each A order: $0.15 on the carton, $0.16 on fill and $0.10 on labor. Across 350 orders, that is $143.50 before its $75 monthly stocking cost, or $68.50 net. F saves $0.67 across only 100 orders, losing $8 after the same stocking cost. At unchanged unit economics, F needs at least 112 qualifying orders per month to break even.
Adding only P therefore produces a four-size regular assortment costing $9,205/month, less than either original candidate, while retaining X. This is a manually constructed comparison, not proof of an optimal catalogue. It gives the team a specific next candidate to trial. F provides tighter fit but does not yet pay for its operating burden.
Supplier terms can change that conclusion. A minimum order quantity, or MOQ, of 1,000 F cartons represents ten months of demand at this mix. Obtain quotes at the quantities actually purchased, including inbound freight, and replace the stocking allowance with the resulting inventory exposure. Check lead times and backup supply. A low price is less useful when shortages repeatedly force larger-box substitutions.
Station capacity also imposes a practical limit. Count slots for flat blanks, reachable working stock and the frequency of replenishment, not just warehouse floor area. Give packers clear carton codes and approved fallback choices. Record actual use: a theoretically available P produces no saving when it is empty, difficult to reach or routinely confused with S. Do not assume a universal penalty per additional size; measure selection mistakes, repacking and walking where they occur.
A custom carton deserves consideration when a stable, recurring order family still has expensive compromises in the available stock sizes. Compare its full landed and operating cost, tooling or setup, qualification, MOQ and obsolete-stock exposure against the next-best acceptable package. A protection requirement can justify a dedicated design even at low volume, but it still needs a replenishment plan.
Trial the candidate without losing sight of exceptions
Begin with recent order records plus a separate peak-period sample. Reconstruct real combinations, including awkward and low-frequency orders. Use these to develop the candidate, then evaluate a separate order sample so the proposal is not judged only on the orders that shaped it.
A bounded operational pilot might use one station across representative operators and shifts for two weeks, provided that period captures the relevant work. Extend it when demand or operating conditions are less frequent. Keep existing fallback packs available. Before starting, define acceptable fit: permitted arrangement, intact protection and separators, closure without forcing or bulging, acceptable gross weight and no prohibited product contact. Record actual packing cycles, material consumption, chosen versus recommended cartons, stockouts and every exception. Weight results back to normal demand if difficult orders were deliberately oversampled.
Packing success alone does not establish shipping protection. ISTA’s testing guidance calls for representative samples, predefined damage criteria and attention to actual distribution conditions. Select appropriate testing for changed packs and continue monitoring shipments; a brief pilot cannot establish a rare damage rate.
For this example, authorize the four-size candidate for that trial, retain X, and defer F. Set the review around its actual qualifying volume and measured savings. Release the revised assortment only after protection is acceptable and the material, labor and inventory savings still cover implementation costs under observed packer behavior.