Buy a cage too small and your dog travels hunched and stressed. Buy one too big and it rattles around the boot, wastes space and gives the dog nothing to brace against under braking. Getting the size right takes ten minutes and a tape measure, so here is exactly how to do it.
One thing to clear up first: a travel cage is sized differently to a home crate. At home, bigger is generally kinder. In a vehicle, a snugger fit is safer, because excess space means the dog gets thrown further in a sudden stop.
Step 1: Measure your dog
You need three numbers. Have some treats ready, because most dogs tolerate a tape measure for about ninety seconds.
Length. Dog standing on all fours. Measure from the tip of the nose to the base of the tail, where the tail meets the body. Do not include the tail itself; that gives you a cage a size too big.
Height. Dog standing. Floor to the top of the head. If your dog has tall, upright ears, measure to the ear tips instead.
Shoulder width. Across the widest point of the shoulders.
Step 2: Turn those into cage dimensions
For vehicle transit, the working rules are:
- Cage length: dog's length plus around 15cm
- Cage height: just above the dog's head height
- Cage width: at least twice the dog's shoulder width
That gives the dog room to stand, sit, turn around and lie down comfortably, without so much spare space that they slide about on the move.
Two adjustments worth knowing. Flat-faced breeds (bulldogs, pugs, boxers) need extra ventilation headroom, so add roughly 10% to all measurements. And if you are buying for a puppy, size for the expected adult dimensions of the breed, not the puppy in front of you, or you will be buying twice.
Step 3: Measure your boot
This is the step people skip, and it is the step that causes returns. A cage has to fit the vehicle as well as the dog.
With the rear seats up and the parcel shelf removed:
Width. Measure at the narrowest point, which usually means between the wheel arches, not across the widest part of the opening.
Depth. From the boot sill to the back of the rear seats, taken at the shallowest point.
Height. From the boot floor to the lowest point of the ceiling or tailgate aperture. Watch for sloping tailgates on hatchbacks; the usable height at the back of the boot is often well below the height in the middle.
A few millimetres matter here. A cage that is 5mm too wide for the wheel arches does not fit, full stop.
The shortcut: search by your vehicle
We have already done the measuring for hundreds of vehicles. Our search by vehicle tool lets you pick your make, model and year and shows you the Dog Box UK cages that fit. It covers everything from a Fiesta to a Defender to a Transit, and it is the fastest way to skip the tape measure entirely on the vehicle side. You will still want to measure your dog.
One dog or two?
If you regularly carry two dogs, a double cage with a central divider is safer and calmer than one shared open space. Each dog gets its own compartment, which stops squabbles, stops one dog crowding the other, and lets you feed or water them separately on long trips. Our double cages come in small, medium and large footprints to suit different boot sizes, and slanted-back versions are available where the tailgate angle demands it.
Common sizing mistakes
Buying on breed alone. A "Labrador-sized" cage does not exist, because Labradors run from 25kg to 40kg. Measure your actual dog.
Forgetting the bedding. A thick mat or bed raises the floor by several centimetres. Account for it in the height.
Ignoring the tailgate slope. Hatchbacks and coupé-style SUVs lose height fast towards the rear of the boot. A slanted-back cage exists for exactly this reason.
Measuring the boot opening instead of the boot. The aperture and the interior are different shapes. Measure inside.
Quick answers
How much bigger than my dog should a travel cage be? Roughly 15cm longer than the dog, just taller than head height, and at least twice the shoulder width. Snug but comfortable.
Is a bigger cage safer? No. In a vehicle, excess space increases how far a dog is thrown under hard braking. Fit the dog, not the boot.
What if my dog is between sizes? Go up, not down, then use bedding to fill the difference.
What if no standard cage fits my vehicle? Ask. We build custom cages in our Devon workshop, and unusual boots are a regular request.
Still unsure? Send us your dog's measurements and your vehicle details via the contact page and we will can help.