A homeware brand shipping ceramic mugs out of Rotterdam kept getting hit with what its carrier called "dimensional weight adjustments" — extra charges tacked onto invoices for boxes that weighed almost nothing but took up a lot of space. Around the same time, the packaging supplier mentioned PPWR's new void space limit. Two problems that looked unrelated turned out to share one root cause: too much empty air in the box. Fix the box, and both problems shrink together.
This is the rare compliance rule that actually pays for itself. Here's how the 50% empty-space ratio works, how to calculate it, and how it maps directly onto the dimensional weight fees carriers already charge you.
The Rule: What "Empty-Space Ratio" Actually Means
PPWR sets a maximum empty-space ratio of 50% for grouped, transport, and e-commerce packaging — no more than half the volume inside a shipped parcel can be empty space (air, oversized void fill, excess room around the product). This is a later-phase obligation, generally applying from around 2030, not part of the August 2026 wave (covered in The August 12, 2026 PPWR Deadline). But the carrier fee problem it solves is already costing you money today, which is the real reason to fix it now.
How to Calculate Void Space Ratio
The math is simple: internal box volume, product-plus-necessary-packaging volume, and the difference between the two.
Void Space Ratio = (Box Internal Volume minus Product+Packaging Volume) divided by Box Internal Volume, times 100
Worked Example
Take a mid-size skincare gift set:
- Shipping box internal dimensions: 30 cm x 20 cm x 15 cm = 9,000 cm3
- Product plus its minimal protective packaging: 20 cm x 12 cm x 8 cm = 1,920 cm3
- Empty space: 9,000 minus 1,920 = 7,080 cm3
- Void space ratio: 7,080 / 9,000 x 100 = 78.7%
That box fails the 50% threshold by a wide margin. Now resize to a box that actually fits the product with reasonable padding:
- Right-sized box: 24 cm x 15 cm x 10 cm = 3,600 cm3
- Same product: 1,920 cm3
- Empty space: 3,600 minus 1,920 = 1,680 cm3
- Void space ratio: 1,680 / 3,600 x 100 = 46.7%
That passes. And it does something else at the same time — it drops the box you're paying to ship.
Why This Is Also a Dimensional Weight Problem
Carriers don't just charge by actual weight. Above a certain size threshold, they charge by dimensional (volumetric) weight — a formula that converts box volume into a "weight" figure, and bills whichever number is higher, actual or dimensional.
Dimensional Weight (kg) = (Length x Width x Height in cm) divided by Divisor
Divisors vary by carrier, commonly in the 4,000-5,000 range for international parcel services — check your own published rate card rather than assuming a fixed number.
Continuing the Worked Example
Using an illustrative divisor of 5,000:
| Box | Dimensions (cm) | Volume (cm3) | Dimensional weight | Actual weight | Billed weight |
|---|---|---|---|---|---|
| Oversized | 30 x 20 x 15 | 9,000 | 9,000 / 5,000 = 1.8 kg | 0.4 kg | 1.8 kg |
| Right-sized | 24 x 15 x 10 | 3,600 | 3,600 / 5,000 = 0.72 kg | 0.4 kg | ~1 kg (rounds to next tier) |
On a single parcel, that's the difference between paying for roughly 1.8 kg and closer to 1 kg — often a full pricing tier, sometimes two. Multiply by volume: a store sending 3,000 parcels a month at an illustrative EUR 1.20 difference per parcel is looking at roughly EUR 3,600 a month, or over EUR 43,000 a year, from oversized boxes alone. These figures are illustrative — run the same math against your own rate card to get your real number.
Right-Sizing: The Fix That Solves Both Problems
- [ ] Audit your top 10 SKUs by volume and measure actual product dimensions
- [ ] Compare against current box sizes in use — flag obvious mismatches
- [ ] Request smaller box options from your supplier, or evaluate auto-sizing machines if volume justifies the cost
- [ ] Recalculate void space ratio for each corrected format
- [ ] Recalculate dimensional weight against your actual carrier rate card
- [ ] Update pack-and-ship instructions so warehouse or 3PL staff default to the right box, not the familiar one
- [ ] Re-run the numbers quarterly as SKU mix changes
Void Fill: The Part People Get Wrong
Void fill — the paper, air pillows, or foam used to stabilize a product — counts toward empty space unless it's doing real protective work. A box stuffed with air pillows around a ceramic mug isn't "full," it's still mostly void; the pillows are filling space that shouldn't exist if the box were sized correctly. The fix isn't more void fill, it's a smaller box. Reserve void fill for irregular shapes or fragile items where right-sizing alone can't stop movement.
Where This Fits Your Broader Packaging Strategy
Void space reduction connects directly to your packaging bill of materials and EPR fee calculations, since some Producer Responsibility Organisations weight fees partly by volume and material mix (more in Mastering Packaging Data). It also affects eco-modulated fees (see Eco-Modulation Explained) and fits the longer transition in Preparing for 2030.
Start With Your Highest-Volume Box
Don't redesign every packaging format this quarter. Pull shipping data for your single highest-volume SKU or box size, run the math above against it, and fix that one first. It's the box you're most exposed on and most likely to save real money on immediately, well ahead of any 2030 requirement (see The August 12, 2026 PPWR Deadline).
For the full text of the empty-space provisions, see the regulation on EUR-Lex. Carrier-specific dimensional weight formulas are published on individual carrier rate card pages — check your own contracted divisor rather than assuming a standard figure.
Frequently asked questions
Is the 50% void space rule already in force?
Not yet. It's a later-phase obligation, generally applying from around 2030, alongside recycled-content minimums and design-for-recycling grades. Core documentation obligations apply from 12 August 2026, but the empty-space ratio itself isn't enforced yet — though right-sizing now already saves you money on shipping.
Does void fill count against the empty-space ratio?
Yes, unless it's genuinely necessary for protecting an irregularly shaped or fragile item. Air pillows and paper filling a box that's simply too large for the product still count as empty space under PPWR's definition — the fix is a smaller box, not more filler material.
What divisor should I use to calculate dimensional weight?
It depends entirely on your carrier and service level — commonly somewhere in the 4,000 to 5,000 range for international parcel services, but always confirm against your own current rate card. Carriers update these periodically, and using an outdated or generic divisor will throw off your cost calculations.
Can right-sizing packaging actually lower my shipping costs, or is that oversold?
It's a real and often significant saving, not just a compliance side effect. Because many carriers bill by dimensional weight above a size threshold, shrinking box volume can drop a parcel into a lower pricing tier even when actual product weight doesn't change at all — the worked example in this article shows the mechanism.
Do grouped and transport packaging follow the same void space rule as individual e-commerce parcels?
PPWR applies the 50% empty-space ratio across grouped packaging, transport packaging, and e-commerce packaging, though the specifics can vary by category. Treat all three as in scope when you're auditing, rather than assuming the rule only touches the final parcel a customer receives.
How often should I re-check my box sizing?
At least quarterly, and any time your product mix changes meaningfully. A box matrix that's optimal for this season's bestsellers can quietly become oversized once your SKU lineup shifts, so treat this as a recurring operational check, not a one-time project.
Compliance glossary
- Void Space Ratio: The percentage of a shipped parcel's internal volume that is empty space rather than product or necessary protective packaging, capped at 50% under PPWR's later-phase requirements.
- Void Fill: Material such as air pillows, paper, or foam used to stabilize a product inside a box; counts as empty space under PPWR unless genuinely needed for protection.
- Dimensional (Volumetric) Weight: A carrier billing calculation that converts a parcel's volume into an equivalent weight figure, used to charge for bulky-but-light shipments.
- Economic Operator: Any business in the packaging supply chain — manufacturer, importer, distributor, or fulfilment provider — that places packaging on the EU market and carries compliance duties.
- Extended Producer Responsibility (EPR): A policy model making producers responsible for the costs and management of their packaging's end-of-life, with some schemes factoring in packaging volume and material mix.
Related reading
- The August 12, 2026 PPWR Deadline: What E-commerce Stores Must Have Ready
- Mastering Packaging Data: How to Build an Accurate Material BOM
- Eco-Modulation Explained: Why Your Packaging Materials Impact Your Fees
- Preparing for 2030: The Long-Term Roadmap for EU Packaging Recyclability
- Future Packaging & Recycling Regulations for eCommerce
