Chargeable weight — the big one
Every courier prices on chargeable weight, which is the greater of two numbers: the parcel's actual weight on the scale, and its volumetric (dimensional) weight. Volumetric weight exists because a big, light box takes up aircraft space that a small, heavy one does not — the carrier has to be paid for the volume it occupies.
The formula used across the Interdoc network is:
- Volumetric weight (kg) = (Length × Width × Height in cm) ÷ 5000
- The parcel is billed on the greater of actual weight vs volumetric weight.
- Maximum 68 kg per piece. Split anything heavier into multiple pieces, each within 68 kg.
Worked example
Say you are sending a box of clothing that measures 40 × 30 × 30 cm and weighs 5 kg on the scale.
| Measure | Value |
|---|---|
| Actual (scale) weight | 5 kg |
| Volume | 40 × 30 × 30 = 36 000 cm³ |
| Volumetric weight | 36 000 ÷ 5000 = 7.2 kg |
| Chargeable weight | 7.2 kg (the greater of the two) |
You would pay for 7.2 kg, not 5 kg. Repack that same clothing into a tighter 35 × 28 × 22 cm carton (21 560 cm³ ÷ 5000 = 4.3 kg) and the box now bills on its 5 kg actual weight — a real saving on exactly the same contents. That is why smart packing is a pricing decision, not just a protection one. See the full method on our volumetric weight guide.
Destination zone
Carriers group the world into zones, and the same 5 kg parcel costs very different amounts to different zones. Distance is part of it, but so are the number of flights, customs complexity and how far the parcel travels on the ground after it lands. As a rough ordering from South Africa:
- Neighbouring / SADC — typically the lowest international rate.
- Europe & the UK — well-served long-haul lanes, competitive rates.
- North America — similar band, sometimes higher on remote states.
- Asia, Middle East, Oceania — varies widely by exact country.
- Remote-area surcharge — a delivery postcode outside the main metros can add a fixed fee regardless of zone.
Speed, fuel & surcharges
Two more levers sit on top of weight and zone:
- Service speed — an express, priority end-of-day product costs more than an economy service that takes a few extra days. If the parcel is not urgent, the slower tier is usually meaningfully cheaper.
- Fuel surcharge — a percentage that moves with global fuel prices, applied to the base rate. It is normal and industry-wide; every carrier levies one.
Other situational surcharges can apply: oversize or over-length pieces, non-stackable or irregular shapes, residential delivery, and the remote-area fee mentioned above. Our surcharges guide lists what can appear and why, and the limits guide covers the size and weight envelope.
Insurance and duties — two separate things
Insurance (optional). Carrier liability by default is limited. If your parcel is valuable, add transit cover — usually a small percentage of the declared value — so you are made whole if the worst happens. It is cheap relative to the goods.
Duties and taxes at destination (not part of the freight). This is the point most senders miss. International courier services are VAT zero-rated in South Africa, so there is no SA VAT on the freight itself. But the destination country will usually charge its own import duty and VAT/sales tax, calculated on the declared value of the goods. Those are separate from what you pay Interdoc and are normally paid by the recipient (importer) before the parcel is released. Warn your recipient to expect them — see our customs and documentation guide for how DAP vs DDP decides who pays.
How to get an accurate quote
Because chargeable weight is the biggest single factor, a good quote starts with good measurements:
- Pack the parcel first, then weigh the finished, sealed box.
- Measure length, width and height in centimetres at the widest points.
- Note the destination city and country — a suburb-level address matters for remote-area fees.
- Enter those into the Interdoc quote tool, or email admin@interdoc.co.za / call 086 999 0559.
If your parcel is documents rather than goods, the picture is simpler and cheaper — read sending documents abroad from South Africa. And before you seal the box, check the packing mistakes that cause customs delays so a cheap quote does not turn into an expensive hold.