Carriers charge on whichever is greater — actual weight or volumetric weight. Enter your parcel's dimensions and weight to see the billable weight, so a shipping quote never surprises you.
What this free tool is great for: a quick, one-off job with no signup — it runs in your browser and there's nothing to manage.
Its honest limit: you can compare up to three scenarios during this visit, but they are not kept after you leave, they won't update as your real numbers change, and this tool does not connect to your live accounts.
A free tool is fine for a one-off. If dimensional weight calculator is a weekly job, these take it off your plate.
Best for small online shops shipping a few parcels monthly
Sounds like you? “Comparing carrier prices parcel by parcel eats my time, and I suspect I overpay on postage.”
Plan that fits: Starter, free; 5¢ a label if you connect your own carrier account
Best for new Shopify dropshippers wanting research and fulfillment together
Sounds like you? “I want product research, competitor store data and fulfillment in one tool instead of several.”
Plan that fits: Lite, $29.99/mo ($19.99/mo billed as $239.88/yr); 7-day trial for $1
Best for small European web shops shipping with several carriers
Sounds like you? “Every shipping day I switch between carrier sites to print labels and handle returns by hand.”
Plan that fits: Lite, €28 a month plus €0.10 a label, up to 400 labels a month; the free plan covers 20 parcels
Best for small sellers shipping up to 100 US parcels monthly
Sounds like you? “I copy each order into a carrier site by hand and still pay close to retail postage.”
Plan that fits: Growth, $19.99 a month, or $14 a month billed yearly; postage is extra
Picked from our review dossiers: who each tool suits, their problem in their words, and the plan that fits. “Try” buttons are affiliate links: we may earn a commission if you sign up, at no extra cost to you. It never changes our verdict.
Ship a large box of something light — pillows, packing foam, empty containers — and you'll often be charged as if it weighed far more than it does. That's dimensional weight, and it catches out almost every business new to shipping. Carriers charge based on either the actual weight or the "dimensional" weight of a parcel, whichever is greater. So a big, light package is billed on the space it occupies, not the grams on the scale.
This calculator works out your dimensional weight so you can see which figure the carrier will actually charge on — and stop being surprised by shipping bills that seem disconnected from what you posted.
Dimensional weight isn't a scam; it's economics. A delivery truck or cargo hold fills up on volume long before it hits its weight limit. A van packed with big boxes of feathers is full but barely loaded by weight — and the carrier still paid to run the whole route. Charging purely by weight would let bulky-but-light shippers use up all the space while paying almost nothing, subsidised by everyone else.
Dimensional weight makes shippers pay for the space they consume, aligning the price with the carrier's real constraint. Once you see it from the truck's perspective, the logic — and the incentive it creates for you to pack tightly — makes sense.
The mechanism is a divisor. You multiply the parcel's length by width by height to get its volume, then divide by the carrier's dimensional factor to convert that volume into a billable weight. A larger divisor produces a smaller dimensional weight, so the divisor a carrier uses matters enormously to your cost. These divisors differ between carriers and between domestic and international services, and carriers have adjusted them over time — usually in ways that increase what shippers pay.
Because the exact figure varies, always check the divisor your specific carrier and service use rather than assuming; a calculator lets you plug in the right one and see the real billable weight.
The process is straightforward once you know the pieces. Measure the parcel's three dimensions — and measure the outside of the packaging, not the product, since that's what the carrier measures. Multiply them for the cubic size. Divide by the carrier's divisor to get the dimensional weight. Then compare that to the actual scale weight, and the carrier bills you on the larger of the two. The one subtlety that costs people money is rounding: carriers typically round dimensions and weights up, so a parcel a fraction over a threshold can jump a whole pricing band. Measuring accurately and knowing the rounding rules keeps you from paying for phantom size.
Dimensional weight punishes a specific profile: light products in large packaging. Think apparel in oversized boxes, lampshades, inflatables, or anything protected by lots of air and padding. For these, the dimensional weight comfortably exceeds the actual weight, so you're paying for volume you didn't need to ship. Dense, heavy items — books, tools, liquids — are usually billed on actual weight and are unaffected. Knowing which side of that line your products fall on tells you immediately whether packaging optimisation is a minor tidy-up or a major cost lever for your business. For bulky-light shippers, it's often the single biggest controllable shipping cost.
The most direct way to cut dimensional-weight costs is to stop shipping air. Oversized boxes with a small product rattling around in a sea of filler are pure wasted volume that you pay for on every parcel. Matching box size closely to the product, using mailers or poly bags for soft goods instead of boxes, and reducing void fill can shrink dimensional weight dramatically — sometimes dropping a parcel into a cheaper band entirely.
Because this cost is paid on every single shipment, even a small reduction in average parcel size compounds across your whole volume into serious savings. Packaging is one of the highest-return things a shipping-heavy business can optimise.
It's worth making the oversized-box cost concrete, because it hides. Every unnecessary centimetre of box adds to the cubic size, which the divisor converts into billable weight, which you pay on every order. A business shipping thousands of parcels a year in boxes one size too big is quietly paying a large, recurring tax on empty space. Worse, oversized parcels can tip into higher service categories or surcharges for large packages.
Auditing your packaging against your actual products — and dropping a box size where you can — often pays back faster than almost any other operational change, precisely because the saving repeats on every shipment forever.
As volume grows, the divisors and rates aren't entirely fixed. Carriers negotiate with shippers who send enough parcels, and better divisors or discounted rates are part of what's on the table. Understanding dimensional weight is what lets you negotiate from knowledge rather than accepting the standard sheet — you can see exactly where your parcel profile costs you and push on the terms that matter for your mix. At scale, even a small improvement in your effective divisor or rate, multiplied across every shipment, is real money, which is why serious shippers treat their carrier terms as something to actively manage, not passively accept.
A number (often 5000 for cm/kg) that converts a parcel's volume into a weight. (L × W × H) ÷ divisor gives the volumetric weight; carriers may use 4000–6000.
Because the parcel is large but light — its volumetric weight exceeds its actual weight, and carriers bill on the greater of the two. Smaller boxes reduce this.
Use the smallest box that fits, and compare carriers — a platform like Sendcloud surfaces the cheapest option and discounted rates.
The pricing behind our reviews is published as an open dataset, with the sentence behind every cost-trap flag and the date it was researched. Free to use with attribution (CC BY 4.0).
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