Box Size Calculator for Cartons, Void Fill and Freight
Enter the item, the quantity per carton and the padding you need. This calculator sizes the smallest box that holds the order, matches it to a carton list you can edit, and shows the void volume, girth and chargeable weight that follow.
Size the Carton, Then Price It
Everything runs in your browser. No dimensions, weights or carton lists leave your device, and nothing is stored after you close the tab.
Item and quantity
Carton list
One carton per line as length x width x height, with an optional name after a comma. Internal dimensions. Replace with your own stock sizes.
Smallest box that holds the order
Recommended carton from your list
| Box | Internal dimensions | Volume | Void | Dim wt at 5,000 / 139 | Dim wt at 6,000 / 166 | Chargeable at 5,000 / 139 | Length + girth | Cost of the extra size |
|---|---|---|---|---|---|---|---|---|
| Tight box, calculated | — | — | — | — | — | — | — | — |
| Recommended carton | — | — | — | — | — | — | — | — |
| Next carton up that fits | — | — | — | — | — | — | — | — |
Divisors are planning figures, not quotes. Use the divisor on your own rate card, and treat rounding as carrier-specific.
This Tool Chooses the Carton the Other Tools Assume
The boundary in one line
The pallet and container calculators take a carton size as input and this page produces it, while the dimensional, volumetric and chargeable weight calculators price a carton you have already chosen.
| Tool | Role | Question it answers | What it gives you |
|---|---|---|---|
| Box size calculator | This page | What carton should these items go in? | Internal carton dimensions, arrangement, void volume |
| Pallet calculator | Next step | How many of that carton fit a pallet? | Cartons per layer, layers, cube utilisation |
| Container loading calculator | Next step | How many pallets or cartons fit a container? | Container fill and units loaded |
| Dimensional and chargeable weight calculators | Pricing | Which weight does the carrier bill for that carton? | Dimensional weight at your divisor, and the higher of the two |
How the Arrangement Is Chosen
The calculator treats the carton as a rectangular block of item positions. It tests every item orientation and every grid that holds the quantity, then keeps the smallest internal volume.
Orientations tested
6 permutations of (L, W, H) Every item sits the same way up. Mixing orientations inside one box is a harder problem and is not attempted here.
Grids tested
nx x ny x nz where nx . ny . nz ≥ N Grids may hold more positions than the order needs. Spare positions count as void, not free capacity.
Internal dimensions
internal_x = nx . a + 2p The same applies on the other axes, where p is padding per side and a is the item dimension on that axis.
- Selection rule: smallest internal volume wins, with combined length and girth as the tie-break.
- Padding applies to all six faces, so each axis gains twice the padding value.
- Quantity is capped at 5,000 items per carton to keep the search instant.
Smallest volume can still be a bad shape
Seven cubes in a column beat a two by two by two block on pure volume, but carry a much larger girth. The girth output exists so you see that before ordering tooling.
The Built-In Carton List, and Where It Came From
There is no universal carton range. These are the sizes the tool ships with, from one supplier's published range of 200 pound (32 ECT) regular slotted cartons, quoted as inside dimensions and converted at 25.4 mm per inch.
| Inside dimensions | Metric | Volume |
|---|---|---|
| 4 x 4 x 4 in | 102 x 102 x 102 mm | 1.05 L |
| 5 x 5 x 5 in | 127 x 127 x 127 mm | 2.05 L |
| 6 x 6 x 6 in | 152 x 152 x 152 mm | 3.54 L |
| 9 x 6 x 6 in | 229 x 152 x 152 mm | 5.31 L |
| 6 x 6 x 10 in | 152 x 152 x 254 mm | 5.90 L |
| 8 x 8 x 10 in | 203 x 203 x 254 mm | 10.49 L |
| 14 x 10 x 6 in | 356 x 254 x 152 mm | 13.76 L |
| 9 x 9 x 12 in | 229 x 229 x 305 mm | 15.93 L |
| 14 x 10 x 8 in | 356 x 254 x 203 mm | 18.35 L |
| 17 x 11 x 8 in | 432 x 279 x 203 mm | 24.52 L |
| 14 x 12 x 10 in | 356 x 305 x 254 mm | 27.53 L |
| 17 x 12 x 12 in | 432 x 305 x 305 mm | 40.11 L |
| 17 x 17 x 17 in | 432 x 432 x 432 mm | 80.51 L |
Source and how to treat it
Sizes read from the published Standard 200# (32 ECT) RSC range at packagingsupplies.com on 14 August 2026. It is a sample spread, not a catalogue, and not a specification for any carrier or retailer. Paste your own list into the carton field before ordering.
The Air You Pay to Move
Void volume is carton internal volume minus item volume, the clearest single number for spotting oversized packaging.
| Where the void comes from | Is it useful? | What to do about it |
|---|---|---|
| Padding you specified | Yes, if the drop test says so | Keep it, and re-test if you reduce it |
| Spare grid positions | No | Change quantity per carton so the grid fills |
| Gap to the next stock carton | No | Add a stock size, or change pack quantity to suit one |
Why Carton Size Is a Freight Decision
Carriers bill the greater of actual weight and dimensional weight. A light, bulky carton costs more than a heavy, compact one, and box choice decides which governs.
Air freight planning
L x W x H ÷ 6000 = kg Centimetres in, kilograms out. The matching imperial divisor is 166 cubic inches per pound.
Express and courier planning
L x W x H ÷ 5000 = kg The same carton gives a higher figure. The matching imperial divisor is 139 cubic inches per pound.
Chargeable weight
max(actual, dimensional) Once dimensional weight passes actual weight, every extra centimetre is a direct cost.
Keep the divisor and the unit together
Divisor 6,000 belongs with centimetres and 166 with inches. Divisor 5,000 belongs with centimetres and 139 with inches. Pairing 6,000 with inches is the most common way a freight estimate comes out wrong.
The Measurement That Triggers Oversize Fees
Girth is the distance around the thickest part of the parcel. Combined length and girth is the longest side plus twice the sum of the other two, and it is what parcel networks check before applying a surcharge.
Formula used here
longest + 2 x (other + other) Applied to every box the calculator reports, after sorting its three dimensions.
One published threshold
108 in maximum, USPS Priority Mail USPS states a maximum combined length and girth of 108 inches for Priority Mail. Read on 14 August 2026.
Everyone else
check your own tariff Thresholds, surcharge names and amounts are carrier-specific and change. No figure is published here for a carrier we have not sourced.
Source
USPS Priority Mail page, read on 14 August 2026: maximum combined length and girth is 108 inches, with girth defined as the distance around the thickest part.
Why the Smallest Box Is Not Always the Cheapest
A carton has to survive a stack, a conveyor and a forklift before it earns the freight saving. Sizing it down changes the load path, not just the volume.
Edge crush
Stacking load travels down the carton corners and edges. Edge crush resistance is a board property, certified by your supplier for the grade you order.
Burst strength
Burst resistance is how the board copes with a concentrated push through the face. It matters when a sharp-cornered item sits hard against the wall.
Contents as structure
Items packed tight carry part of the stacking load. Items floating in void fill do not, so the board alone holds the pallet above.
Failure cost
One crushed carton writes off the units inside, triggers a re-ship and a refund, and costs more than the void fill saved across the order.
- Ask your supplier for the certified grade of the exact carton you buy.
- Re-test after any size reduction. A shorter carton changes the load per carton.
- Check the fit at the tightest tolerance. Cartons are made to a tolerance, not a fixed size.
- Keep a minimum clearance for fragile items whatever the volume maths says.
Three or Four Carton Sizes, Not Twenty
A small carton range trades a little void volume for a lot of operational speed. Test the trade directly by editing the carton list above.
| Dimension of the decision | Wide range, many sizes | Narrow range, three or four sizes |
|---|---|---|
| Void volume per order | Lower, because each order gets a close fit | Higher, because orders round up to the next size |
| Pick and pack speed | Slower: packers choose between many options | Faster: the choice is close to automatic |
How to choose the three or four
Run your top order profiles through the calculator and keep the sizes that recur. A size that stacks cleanly onto your pallet beats one that shaves a little void.
Carton Size Decides Pallet Fit and Container Fit
Cube utilisation is a whole-chain number. A carton chosen only for the parcel network can waste more space on a pallet and in a container than it saved.
- A carton whose footprint divides the pallet footprint cleanly beats a slightly smaller one that does not.
- Check carton height against your maximum loaded pallet height before finalising.
- Container fill follows pallet fill, so a carton change reaches sea freight cost.
Twelve Skincare Bottles, Los Angeles to Chicago
The arrangement
The search returns a three by four by one grid with the bottles upright. Internal size is 220 by 280 by 190 mm: 6,480 cubic centimetres of product in an 11,704 cubic centimetre box, so 44.6 per cent is void.
| Box | Internal dimensions | Volume | Void | Dim wt at 5,000 | Dim wt at 6,000 | Chargeable at 5,000 | Length + girth | Versus the tight box |
|---|---|---|---|---|---|---|---|---|
| Tight box, calculated | 220 x 280 x 190 mm | 11,704 cm3 | 44.6% | 2.34 kg | 1.95 kg | 3.71 kg | 1,100 mm / 43.3 in | Baseline |
| 9 x 9 x 12 in carton | 229 x 229 x 305 mm | 15,928 cm3 | 59.3% | 3.19 kg | 2.65 kg | 3.71 kg | 1,219 mm / 48.0 in | No change |
| 14 x 10 x 8 in carton | 356 x 254 x 203 mm | 18,354 cm3 | 64.7% | 3.67 kg | 3.06 kg | 3.71 kg | 1,270 mm / 50.0 in | No change |
| 17 x 11 x 8 in carton | 432 x 279 x 203 mm | 24,515 cm3 | 73.6% | 4.90 kg | 4.09 kg | 4.90 kg | 1,397 mm / 55.0 in | +1.19 kg, +32% |
| 14 x 12 x 10 in carton | 356 x 305 x 254 mm | 27,530 cm3 | 76.5% | 5.51 kg | 4.59 kg | 5.51 kg | 1,473 mm / 58.0 in | +1.80 kg, +48% |
Where the bill actually flips
Actual weight is 3.71 kg, and the tight box plus the next two stock cartons all still bill on it. The 17 by 11 by 8 inch carton is where volume takes over, at 4.90 kg chargeable.
Take the Carton Size Through the Rest of the Chain
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