Booking a reefer isn't just picking a refrigerated box and moving on — the size decision carries more weight than it does for a dry container, because a reefer's refrigeration unit needs clear airflow around the cargo to actually hold temperature. Load a 40RF too densely and the unit can't circulate cold air through the stack; book a 20RF for a shipment that's genuinely bulky and you're paying for a second box you didn't need. Getting reefer sizing wrong risks the cargo itself, not just the freight bill.
This guide compares the 20RF and 40RF on payload, volume, and the airflow and power considerations that come with cold-chain equipment, so you can match the box to the shipment before you book.
20RF vs 40RF specs at a glance
A 20RF reefer holds up to 27,400 kg and 28.3 CBM. A 40RF holds up to 29,100 kg and 59.3 CBM — roughly double the volume for about 6% more payload capacity. That gap is smaller in relative terms than the equivalent dry-container jump, because a reefer's insulated walls and refrigeration unit already eat into usable space in both sizes. The core decision still comes down to whether your cargo is weight-limited or space-limited, plus how much airflow clearance your product needs around the load.
| 20RF (20ft reefer) | 27,400 kg max payload / 28.3 CBM max volume |
|---|---|
| 40RF (40ft reefer) | 29,100 kg max payload / 59.3 CBM max volume |
Compare that to dry equipment: a 20GP carries 28,200 kg against 33.2 CBM, and a 40GP carries 28,750 kg against 67.7 CBM. Reefer boxes lose a few CBM of usable volume to the refrigeration unit and insulated lining, which is why a 20RF's practical fill point often lands a little lower than shippers expect coming from dry-container experience.
The weight-vs-volume trade-off for reefer cargo
As with dry equipment, the deciding factor is your cargo's density in kilograms per CBM — but reefer cargo runs a wider range than general cargo, from dense frozen protein to bulky fresh produce packed in vented cartons. Frozen meat, seafood, and chemicals in drums tend to be dense and can approach a reefer's weight limit well before the box fills. Fresh produce, flowers, and pharmaceuticals in ventilated cartons tend to be bulky and fill the cubic space first, often with meaningful payload allowance still unused.
A rough guide:
- Above roughly 900 kg/CBM (frozen protein, chemicals, dense packaged goods), a 20RF is likely to hit its weight limit before the box fills — splitting across two 20RF units can outperform overloading one.
- Below roughly 400 kg/CBM (fresh produce in vented cartons, flowers, light pharmaceuticals), a 40RF fills on cubic space with payload capacity to spare.
- In between, most reefer cargo fits either size, and the call comes down to how much clear airflow space your product needs and the cost per CBM on your lane.
Run your carton or pallet counts through the free cargo calculator to get total CBM and gross weight before you compare box sizes — it computes the numbers from your dimensions, not a price estimate.
Airflow and power: the reefer-specific factor
Unlike a dry box, a reefer's refrigeration unit needs unobstructed airflow through and around the cargo to hold temperature evenly, which means "fitting" cargo into the volume isn't the whole story. Cargo stowed too tightly against the walls or stacked without gaps blocks the cold-air return path, creating warm pockets even when the unit itself is working correctly.
- 20RF: shorter airflow path, which can make even circulation easier for uniform, well-stowed loads, but less forgiving of overpacking given the smaller volume.
- 40RF: longer airflow path down the length of the container, so correct stowage — gaps for air return, no cargo blocking the rear bulkhead — matters more at this length.
- Both sizes run on a genset or reefer plug power for the length of the voyage; confirm power availability and any plug-in requirements at transhipment ports regardless of size, since a gap in power is a gap in temperature control.
Ventilation settings, temperature set-point, and humidity control are cargo-specific and confirmed at booking — they don't change based on container size, but the stowage plan that keeps airflow clear does. For high-value frozen or pharmaceutical loads, it's worth confirming cargo insurance terms for temperature-sensitive claims before booking, since a spoilage claim typically turns on proof of continuous temperature control rather than the container size itself.
20RF vs 40RF: side by side
| Factor | 20RF | 40RF |
|---|---|---|
| Max payload | 27,400 kg | 29,100 kg |
| Max volume | 28.3 CBM | 59.3 CBM |
| Best for | Dense frozen/chilled cargo, chemicals, smaller volumes | Bulky fresh produce, pharmaceuticals, larger volumes |
| Airflow path | Shorter, less margin for overpacking | Longer, stowage discipline matters more |
| Terminal handling | One THC per box, reefer plug-in typically applies | One THC per box, reefer plug-in typically applies |
Neither size is categorically cheaper — the ocean FCL rate for a 40RF is higher in absolute terms than a 20RF but is usually lower per CBM once volume justifies the bigger box. That crossover shifts by lane, carrier, and season, so confirm actual rates for both sizes on your route rather than assuming.
When a 20RF is the right call
Choose a 20RF when cargo is dense enough to approach the weight limit well before the box fills, or when total volume doesn't justify 40RF space you won't use. Typical cases:
- Frozen meat, seafood, or dairy where weight, not space, is the binding constraint.
- Chemicals or pharmaceuticals in drums or dense packaging.
- Smaller lots in the roughly 12–24 CBM range, where a 40RF would mean paying for unused cubic space and a longer airflow path than the load needs.
When a 40RF is the right call
Choose a 40RF when cargo is bulky enough that cubic space, not weight, is the constraint — fresh produce in vented cartons, flowers, or larger pharmaceutical shipments that need volume more than payload headroom. A 40RF gives roughly double the CBM of a 20RF for only a modest increase in payload allowance, which is the entire case for stepping up once volume crosses the 20RF's practical fill point — provided the stowage plan keeps the airflow path clear along the full length of the box.
How to decide for your shipment
- Get total weight and CBM. Run your carton or pallet counts through the free cargo calculator rather than estimating.
- Check density. Divide weight by CBM — high density points toward a 20RF (or splitting across units), low density points toward a 40RF.
- Confirm airflow clearance, not just cubic fit — reefer stowage needs gaps for air circulation that dry cargo doesn't.
- Compare cost per CBM on your actual lane, since the 40RF's per-CBM economics don't hold on every route.
- Check power and plug-in availability at any transhipment port before booking, regardless of box size.
Reefer sizing carries more consequence than a dry-box decision, since a poor fit can mean spoiled cargo rather than just an inefficient container. Holo Cargo's operators confirm weight, volume, and stowage plan against the right reefer size before the quote is finalised, working alongside the carrier's reefer handling requirements at both ends of the move. See the full special cargo capabilities for reefer, dangerous goods, and oversized freight together.
