The switch from stock to custom packaging is one of those decisions that businesses put off until they're spending enough on packaging to make the delay feel genuinely costly. The threshold where custom starts to make financial sense is lower than most buyers assume, and the hidden costs of stock sizing are higher than they typically account for.
What stock packaging is actually costing you beyond the unit price
Stock boxes from a distributor's catalogue are available in packs of 25 to 100, available next-day, with no tooling commitment. The per-unit cost looks reasonable. The problem is dimensional efficiency.
Standard stock sizes are designed to serve a broad range of products adequately, not to fit any specific product well. For most products, you'll end up with a stock box that's 25-40% larger by volume than your product requires. That difference costs you in several ways at once: more void fill material to stop the product moving, higher parcel weight, worse performance on dimensional weight carrier pricing, less efficient pallet loading, and higher EPR fees because you're paying levy on more packaging weight than you need to use.
Stock packaging is the right answer when your volumes are genuinely low (under 300-400 boxes per month), when your product range means you'd need multiple custom sizes, or when you're in an early stage and don't yet know what dimensions will settle at. Outside those scenarios, the ongoing inefficiency cost is worth calculating properly.
When custom packaging pays for itself
Custom corrugated means manufacturing to your specified internal dimensions, at the board grade your product actually needs, in agreed run quantities. For plain (unprinted) corrugated, minimum order quantities typically start at 500-1,000 units from most UK corrugated converters. The unit cost, once you're at those volumes, is often lower than equivalent stock because you're not paying the distributor's margin and you're not over-specifying the board grade.
The dimensional efficiency gain is where the real return comes from. An e-commerce business shipping 1,000 boxes per month that switches from a stock box with 35% excess volume to a custom right-sized box typically saves on void fill material, drops some parcels out of higher carrier DIM weight brackets, and improves pallet use. Combined, those savings commonly reduce total per-unit packaging and delivery cost by 15-20%, which is a meaningful number across annualised volume.
For products moving through courier networks, the carrier pricing impact alone can justify the switch. Dimensional weight pricing means a box that's 5cm too large in any dimension may push every parcel into the next pricing band.
The calculation most buyers skip
Before deciding, do this properly rather than estimating.
Measure your current stock box dimensions and calculate its internal volume. Measure your product in its most common packing configuration and calculate the ideal box dimensions. Work out the difference in volume as a percentage.
Then multiply that percentage by your current packaging spend including void fill, and by any carrier cost uplift from dimensional weight. That's the annualised cost of staying with stock. Compare that to the tooling cost (usually zero for plain corrugated) and minimum order commitment for a custom equivalent.
For a business spending £2,000 per month on packaging and carrier costs, a 20% efficiency gain from right-sizing is £400 per month, or nearly £5,000 per year. Custom corrugated at 500 units per run has almost no capital cost attached to it. The business case is usually clear once the numbers are written down.
When getting custom quotes, provide exact internal dimensions in millimetres, the product weight, a brief description of what's inside (fragile, flat, stacked), and your estimated monthly quantity. A good corrugated supplier will recommend an appropriate board grade rather than just quoting what you asked for. If they don't engage with the specification detail, find one that does.