Cat Door Buying Guide: Which Cat Flap Is Right for You?

October 20, 2026

A cat door gives your cat the freedom to come and go on their own schedule, whether that means stepping into a catio, popping out to a screened porch or reaching a litter box in the laundry room. The tricky part is choosing the right one. This guide compares the three main types of cat flap, shows you how to measure your cat, and covers where to fit a cat door so it actually gets used.

The three main types of cat door

1. Locking cat flaps (manual)

The classic cat flap is a framed, swinging door with a dial or slider that sets the mode. A 4-way locking flap lets you choose in only, out only, both ways or fully locked. That's handy at night, at the vet's request or when you want your cat to come in but not go back out.

Best for: doors, walls and catio panels where you want simple, reliable access. Our 4-Way Locking Cat Flap adds a weatherproof flap with a brush seal to keep drafts out, and comes in four sizes and three colors.

2. Screen door cat flaps (magnetic)

If your catio or porch connects through a window or door screen, you don't need to cut wood or glass. A screen door flap fits into the mesh and uses magnets to swing shut behind your cat, which also helps keep insects out.

Best for: screened windows, sliding screen doors and screened porches, especially in rentals. See our Magnetic Screen Door Cat Flap, which is lockable and self-closing.

3. Smart selective-entry flaps

Selective-entry flaps unlock only for the cats you register, so the neighbor's cat, strays and wildlife stay outside. Depending on the model, they recognize your cat's implanted microchip, a sensor tag on the collar, or both.

Best for: homes with visiting cats, raccoons or other animals that might wander in, and multi-pet homes where only some pets should go out. Our Microchip Smart Cat Flap reads both your cat's microchip and the collar tags it comes with (2 or 4), so it works for chipped and unchipped cats. It also has lock modes and a large XL frame that suits big cats.

Quick comparison

Simplest and most affordable: 4-way locking flap.
No cutting, renter-friendly: magnetic screen door flap.
Keeps other animals out: smart selective-entry flap.
Largest cats: choose the XL size of any style and check the opening against your measurements.

How to measure your cat

Width: measure across your cat's shoulders or the widest part of the body. Choose a flap with an opening at least 1 inch (2.5 cm) wider.
Height: measure from the top of the shoulders to the bottom of the chest. The opening should be taller than this.
Belly height: measure from the floor to your cat's belly. This is roughly where the bottom of the flap opening should sit, usually around 4 to 6 inches (10 to 15 cm) from the floor, so your cat can step through without crouching or jumping.

If you're between sizes, go bigger. A flap that's too tight is the most common reason a cat refuses to use it.

Where to install a cat door

Interior or exterior doors: the most common spot. Hollow-core doors need a frame liner or a flap with a tunnel that covers the cut edge.
Walls: great for connecting a catio. A wall install needs a tunnel that matches the wall thickness. Check for pipes and wires first, or ask a professional.
Windows and screens: a screen flap or a panel insert gives access to a window box catio without permanent changes.
Catio panels: many catios have mesh or wooden walls where a flap can be mounted, so your cat can move between sections.

How to teach your cat to use a cat door

Start with the flap propped open. Tape or tie it up so your cat sees a clear opening.
Use treats and praise. Put a treat on the other side, or have someone call your cat through.
Lower the flap gradually. Once your cat walks through confidently, let the flap rest partly closed, then fully closed.
Be patient. Some cats learn in a day; others need a week or two. Never push a cat through, as a scare can set training back.
For smart flaps, register your cat's microchip or tag first. If you use a collar tag, let your cat wear it for a few days before training, so it feels normal.

Safety tips

Use a breakaway collar if your flap needs a collar tag.
Make sure the cat door leads somewhere safe, such as a secure catio, an enclosed porch or an indoor room, rather than straight onto a busy street.
Use the lock at night if you don't want your cat out after dark.
Check the flap regularly for cracks or worn seals.

A cat door plus a catio

Pairing a cat door with a catio gives your cat safe outdoor time whenever they like, with no roaming and no waiting at the door. If you're still choosing a catio, read Catio or Cat Enclosure: Which Fits Your Home? or browse all our cat doors and flaps.

Ordering from Catio & Co.

We ship to the US, UK, Canada, Australia and New Zealand, with free tracked shipping on orders over $50. Most orders arrive in 7–15 business days, and you have 30 days to return an item if it isn't right for your cat.

Frequently asked questions

What size cat door do I need?

Measure your cat's widest point and choose a flap opening at least 1 inch wider. Large breeds like Maine Coons usually need an XL flap.

Do smart cat flaps work with microchips?

Many do. Ours reads both implanted microchips and the collar tags that come with it. If you buy a different model, check its description, as some only work with tags.