There is a formula for this. It is published by IATA, every airline that carries animals works to it, and it takes four measurements and about two minutes. Almost nobody uses it, which is why crates get refused at check-in and why owners pay for space their animal does not need.
This page gives you the calculation, a worked example, and an honest answer to the question everyone asks, which is whether to round up.
Take Four Measurements
Measure the animal standing normally, not sitting and not stretched out. If more than one animal will share the container, measure the largest.
| What to measure | |
|---|---|
| A | Length from the tip of the nose to the base of the tail. Not the end of the tail, the root of it. |
| B | Height from the ground to the elbow joint. |
| C | Width across the shoulders, or the widest point of the animal if that is wider. |
| D | Height from the floor to the top of the head, or to the ear tip if the ears are higher. |
Then Do the Arithmetic
IATA sets the minimum internal dimensions as follows.
| Dimension | Formula |
|---|---|
| Length | A + ½B |
| Width | C × 2 |
| Height | D, plus the depth of the bedding you will put in |
| Snub-nosed breeds | Add 10% to the container |
| Two animals sharing | Width becomes C × 3 |
| Three animals sharing | Width becomes C × 4 |
Two details in that table do most of the damage when they are missed.
The first is that these are internal dimensions. Crates are advertised by their external measurements, and the difference between the two on a large plastic kennel can be a couple of inches on every axis. Buying to the number you calculated, without checking that the number is the inside of the box, is the most common sizing error there is.
The second is the bedding. The height is the animal’s standing height plus whatever it is standing on. An absorbent pad is not deep, but a crate that fits exactly with an empty floor does not fit once the floor is covered.
A Worked Example
A medium dog measuring 60 cm from nose to tail root, 30 cm from the ground to the elbow, 22 cm across the shoulders and 50 cm to the top of the head:
- Length: 60 + 15 = 75 cm
- Width: 22 × 2 = 44 cm
- Height: 50 cm plus bedding, so call it 53 cm
That is the minimum internal box. The crate to buy is the smallest one on the shelf whose internal dimensions meet or exceed all three. Not the one that looks about right, and not the next one up from that.
If the dog is a snub-nosed breed, add ten percent and the answer becomes roughly 83 by 48 by 58 cm.
Should You Round Up? The Honest Answer
The common advice is that when you are between two sizes you should go up. That advice exists because an undersized crate is refused at the counter and a move fails on the day, which is the worse of the two failures. As a rule of thumb for someone who has not measured, it is reasonable.
It is also expensive, and it is worth knowing why before you follow it. Air cargo is priced on dimensional weight, which is calculated from the crate’s outside measurements rather than from what the animal weighs. A crate one size larger can push a booking into a higher band and cost more than the difference between two routings. Sizing up is not a free kindness. It is a line on the invoice.
The resolution is not to pick a side, it is to stop guessing. Measure the animal, run the formula, and buy the smallest crate whose internal dimensions clear it. Then rounding up is not a judgment call you are making under uncertainty, it is simply what happens when the shelf has no size between the one that is too small and the one that fits, and you will know exactly what that step is costing you.
Where the animal genuinely sits on a boundary, round up. A refused crate on the day costs more than a higher weight band, and the animal has to be able to stand, turn around and lie down naturally in it regardless of what the arithmetic says.
When Animals Can Share, and When They Cannot
The rules here are specific and they are set by weight rather than by relationship.
- Any animal over 14 kg must be crated individually. There is no exception for a bonded pair.
- Up to two adult animals of comparable size, each 14 kg or under, that are used to living together may share a container.
- Puppies and kittens may share if they are from the same litter, under six months old, no more than 14 kg each, and no more than three in one container.
- Some national rules override all of that and require individual crating anyway, unless the consignment is a litter over eight weeks old traveling with its mother.
IATA is blunt about the reason, and it is worth repeating to owners who want to keep two animals together for comfort: animals may become stressed and aggressive when flying, and animals from the same household are not exempt from that. Sharing a crate is permitted in narrow circumstances rather than encouraged.
Why the Crate Decides the Price
This is the part that surprises owners, and it is the reason to measure before you shop rather than after.
The airline charges on the greater of the actual weight and the dimensional weight, and the dimensional weight comes from the crate’s outside measurements. So the box, not the animal, usually sets the number. Two dogs of identical weight in different crates produce different quotes, and a quote given before anyone has measured is an estimate of an estimate.
The figures for what a move costs live on one page so they stay current in one place: see our dog shipping cost guide and the cat equivalent.
For a large dog the crate is the single most expensive decision in the move, and the constraints stack up differently. That case is covered in flying with a large dog.
Frequently asked questions
How do I know what size crate my dog needs?
Measure four things: nose to tail root, ground to elbow, width across the shoulders, and floor to the top of the head or ear tip. The minimum internal crate is then length A plus half B, width C times two, and height D plus bedding. Snub-nosed breeds need a container ten percent larger.
Are crate sizes measured inside or outside?
The formula gives internal dimensions, and crates are sold by external ones. Check the manufacturer’s internal measurements against your calculation, because on a large kennel the difference runs to a couple of inches on every axis.
Can my two dogs travel in one crate?
Only if both are 14 kg or under, of comparable size, and used to living together. Any animal over 14 kg must be crated individually, and some countries require individual crating regardless. The width formula also changes: two animals need C times three rather than C times two.
Should I buy a bigger crate so my pet is comfortable?
Comfort is defined by the standard rather than by extra room: the animal must be able to stand and sit erect, turn around normally, and lie in a natural position. Beyond that, extra space is charged for, because cargo is priced on the crate’s outside dimensions. Buy the smallest crate that clears the formula.
Does a soft carrier work for the hold?
No. A soft-sided carrier is a cabin item. An animal traveling in the hold needs a rigid container built to the IATA standard, which covers construction, ventilation, fastenings and labeling as well as size. Those are set out in our guide to airline crate requirements.
Sources
- IATA, Traveler’s Pet Corner. The measurement definitions, the container formula, the ten percent uplift for snub-nosed breeds, the multiple-animal width calculations and the 14 kg individual-crating threshold. Container Requirements 1, LAR 2026 edition.
Last updated 8 September 2026