Methodology

Volumetric and dimensional weight

One calculation with two names. Multiply the three outer dimensions, divide by the carrier's divisor:

volumetric weight = (L × W × H) ÷ divisor

The divisor is a pricing policy, not a constant. In centimetres and kilograms the express standard is 5000, which is 200 kg per cubic metre. In inches and pounds it is usually 139. Air freight uses 6000 metric, or 167 kg per cubic metre. Australia Post uses 4000.

We compute in the carrier's own unit system rather than converting first. Converting centimetres to inches and then dividing by 139 drifts a percent or two from the carrier's own quote, which is enough for a user to lose trust in the tool. If you enter centimetres we use the metric divisor; if you enter inches we use the imperial one.

Two carriers apply thresholds rather than charging dimensional weight on everything. USPS applies it only to parcels that exceed one cubic foot (1,728 in³) — so a 12-inch cube, at exactly 1,728, is not affected at all — and since 12 July 2026 it rounds every measurement up to a whole inch before multiplying, with nonrectangular parcels multiplied by 0.785. Australia Post applies its cubing rule above 0.25 m³. Both rules are read from DMM 113.1.3.

Published rates, and why only USPS has them

One carrier on this site returns a real price rather than asking for yours. USPS publishes its complete tariff openly in Notice 123, so we parse it: Ground Advantage, Priority Mail and Priority Mail Express, each in retail and commercial, 431 weight bands across nine zones, effective 12 July 2026. Because all six tables are loaded, the calculator can price one parcel against every service at once — which is how you find out that under this notice Ground Advantage is cheaper than Priority Mail at every single weight and zone, and that the premium you pay for Priority Mail buys delivery days rather than a better rate.

DHL, FedEx and UPS do not. Their rate cards sit behind an account or a bot wall — FedEx returned a permission interstitial to every automated request we made. For those carriers the calculator takes the rate you were quoted, which is honest, and still gets right the part that goes wrong in practice: the chargeable weight that rate is multiplied by, and the surcharges stacked on top.

The tables are generated, never typed. Every row must clear six checks before it is emitted: exactly nine zone prices, prices that never fall as the zone rises, prices that never fall as the weight rises, every value inside a plausible band for that service, the exact set of weight bands with nothing missing and nothing invented, and commercial undercutting retail at every comparable band. The completeness check exists because an earlier version of the parser silently dropped the 12 oz row — the surviving rows were all internally consistent, so nothing else caught it. Absence is the failure mode that validation misses unless you go looking for it.

The source PDF is kept alongside the parser and its SHA-256 is recorded in the generated file, so the numbers on this site can be traced back to one specific document rather than to "the USPS website". A single command re-reads the PDF and fails if what is published here has drifted from what the notice says.

The lookup refuses rather than extrapolates. Ask for 80 lb on a table that stops at 70 and you get an error, not a guess: the table ends because the service ends.

Chargeable weight

chargeable = ceil(max(actual, volumetric) ÷ increment) × increment

The greater of the two, pushed up to the carrier's billing increment. Most express carriers bill in 0.5 kg steps up to 30 kg and 1 kg steps above it, so a consignment calculating at 30.2 kg bills at 31.

For multi-piece shipments, volumetric weight is calculated per piece and then totalled — carriers measure each box, not the shipment. This is why splitting one heavy box into two light ones usually costs more.

Girth and length plus girth

girth = 2 × (second-longest + shortest)
length + girth = longest + girth

The longest side is always the length, whichever field you typed it into, because that is how a carrier measures. We sort the three dimensions before applying the formula.

Air freight and mode conversion

Different modes convert volume to weight at different rates. The same cubic metre is billed as:

• 167 kg by air freight, from the IATA 1:6000 ratio
• 200 kg by an express courier, from 1:5000
• 333 kg by European road groupage, from 1:3
• 1,000 kg by sea LCL

Sea LCL revenue tonnes

revenue tonnes = max(CBM, weight in tonnes)

LCL is not billed on a divisor. It is quoted per revenue tonne — whichever is greater of one cubic metre or 1,000 kilograms. Because most consumer goods are less dense than that, LCL almost always bills on volume.

Pallet and container packing

We do not divide one volume by another. For each of the two base orientations of the carton footprint, we fill the main block, then pack the two leftover strips in the rotated orientation:

main block   = floor(deckL ÷ a) × floor(deckW ÷ b)
length strip = floor((deckL − nx×a) ÷ b) × floor(deckW ÷ a)
width strip  = floor((nx×a) ÷ b) × floor((deckW − ny×b) ÷ a)

The two strips are disjoint by construction, so the total is always physically achievable. We take the better of the two starting orientations. The result is a floor, never an optimistic estimate — which is the opposite of what volume division gives you.

Layers come from usable height divided by carton height, and the whole thing is then capped by the pallet or container weight limit if that binds first. We tell you which constraint bound.

LTL freight class

density = weight (lb) ÷ (L × W × H in inches ÷ 1728)

Density in pounds per cubic foot maps to an NMFC class on the 13-tier scale introduced by NMFTA Docket 2025-1 on 19 July 2025. Measure the handling unit as loaded, including overhang and the pallet itself.

Density is one of four NMFC factors. Stowability, handling and liability can move a class independently, so treat a calculated class as an opening position rather than a settled fact.

Customs duty and import tax

The sequence matters more than the rates, and it differs by country.

customs value = goods + freight + insurance   (CIF countries)
customs value = goods                         (FOB countries, incl. the US)

duty          = customs value × duty rate
levies        = per-country, applied to their own base
taxable value = goods + freight + insurance + duty + levies   (typical)
import tax    = taxable value × tax rate

Import tax is charged on the value after duty in almost every country, so the two compound. Calculating them independently and adding the results understates the bill — the most common error we found in free duty calculators.

India stacks three levies in a fixed order: basic customs duty on CIF, then social welfare surcharge at 10% of the duty (not of the goods), then IGST on the accumulated total.

De minimis thresholds are tested against the goods value in the destination currency. If your input currency differs and you have not supplied an exchange rate, we say so and assume no relief rather than guessing.

Marketplace fee stacks

The fee base differs by marketplace and is a frequent source of error. eBay charges its final value fee on the item plus postage plus sales tax. Etsy charges its transaction fee on the item plus postage. Amazon charges the referral fee on the item plus shipping and gift wrap. Shopify charges no commission at all.

Tiered categories step the rate at price points rather than applying one rate — Amazon's clothing category runs 5% at or below $15 and steps upward from there. Minimum fees and closing fees are applied after the percentage.

Where a marketplace charges VAT on its own fees to non-registered sellers, that VAT is applied to the total of all marketplace fees, and it is not reclaimable.

Amazon FBA fulfilment

Size tier comes from the packaged dimensions and weight. Small standard is up to 18 × 14 × 8 inches and 1 lb; large standard is up to 20 lb with a longest side up to 18 inches; large bulky runs to 37 inches or 50 lb.

Above small standard, billable weight is the greater of unit weight and dimensional weight on a 139 divisor. The fee then depends on the weight band and — since 15 January 2026 — on which of three price bands your selling price falls into. The 3.5% fuel and logistics surcharge introduced on 17 April 2026 is applied to the resulting fulfilment fee, not to the sale price.

Profit, margin and break-even

net revenue = price ÷ (1 + tax rate)   when the price includes tax
net profit  = net revenue − platform fees − product costs − returns − advertising
net margin  = net profit ÷ net revenue
ROI         = net profit ÷ (COGS + inbound)

Margin is measured against net revenue so it stays comparable across tax regimes. Commission is still charged on the gross price the buyer paid, because that is what marketplaces actually do.

Return cost is spread across every unit sold, not per unit returned. Per return we count the handling cost, the refund administration fee, the proportion of stock that cannot be resold, the outbound fulfilment fee you do not get back, and whatever share of commission the marketplace keeps.

Break-even price and target-margin price are solved numerically by bisection rather than algebraically. Fee schedules have tiers, minimums and floors, so a closed-form solution would break silently the moment we added one. The solver runs sixty iterations, which converges well inside a cent.

Break-even ACOS

contribution margin = net revenue − all costs except advertising
break-even ACOS     = contribution margin ÷ price
break-even ROAS     = price ÷ contribution margin
max CPC             = contribution margin ÷ (100 ÷ conversion rate)

Safety stock and reorder point

safety stock  = z × √(leadTime × σ_demand² + demand² × σ_leadTime²)
reorder point = demand × leadTime + safety stock
EOQ           = √(2 × annual demand × order cost ÷ holding cost)

Safety stock uses the statistical form, combining demand variability and lead-time variability, with z taken from your target service level — 1.645 at 95%. If you do not supply standard deviations we fall back to a buffer of 25% of lead time and say clearly that it is a rule of thumb rather than a service-level guarantee.

Lead time includes warehouse receiving time, because stock sitting in a receiving queue is not sellable stock.

Rounding and precision

Money rounds half away from zero at two decimal places, which is what fee schedules assume. Rounding is done through exponent shifting rather than multiplying by a power of ten, so 1.005 rounds to 1.01 rather than to 1.00 — a binary floating-point artefact that quietly costs a cent in a surprising number of calculators.

Weights are carried at full precision through the calculation and rounded only for display, so intermediate rounding never compounds.

How this is verified

The calculation engines are covered by a test suite that checks them against published worked examples: DHL's own 40 × 30 × 20 cm example returning 4.8 kg, the USPS 14 × 12 × 12 inch carton moving from 13 lb to 15 lb across the July 2026 divisor change, and the 12-inch cube correctly falling below the one-cubic-foot threshold, the UK VAT-on-duty sequence, India's three-levy stack, eBay's fee base including tax, and Amazon's three price bands. Where our answer would differ from a carrier's published example, that is a bug and we would like to hear about it.