How to fit a porthole in a door
Updated: October 2026
You are about to mark a circle on a door or a shed panel, and the expensive mistake is the hole. How to fit a porthole in a door starts with the leaf: thickness, whether this is a fire door, and whether the screws are in the box. This page is the sequence for a normal interior door that is not a fire door, and for an opening portlight in a panel you are allowed to alter. The rows are on the [porthole comparison](/hub/door-and-window-security/porthole). Peter F. used the maker's fitting order and the listings saved on 19 October 2026. We did not fit a unit. A qualifying purchase can earn a commission at no extra cost to you.
You are about to mark a circle on a door or a shed panel, and the expensive mistake is the hole.
You are about to mark a circle on a door or a shed panel, and the expensive mistake is the hole. How to fit a porthole in a door starts with the leaf: thickness, whether this is a fire door, and whether the screws are in the box. This page is the sequence for a normal interior door that is not a fire door, and for an opening portlight in a panel you are allowed to alter. The rows are on the porthole comparison. Peter F. used the maker's fitting order and the listings saved on 19 October 2026. We did not fit a unit. A qualifying purchase can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Opens | Stated thickness | Fixings | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  MLS MLS porthole B4000 | Not stated as opening | Door leaf 40 mm, plus or minus 2 mm | Mounting material included | 7.8 | about £77.42 | View offer |
 HouYeen HouYeen black opening porthole | Yes, two fittings loosen | n/a | Screws not included | 8.6 | about £30.99 | View offer | |
| Best value |  GAESHOW GAESHOW black boat porthole | Yes | n/a | Screws not included | 8.0 | about £29.99 | View offer |
On this page
Before the jigsaw
Take the door off its hinges and lay it flat only after three answers are yes. The thickness matches the product. The door is not a fire door. The fixings are already in the room. For the MLS B4000 the listing states 40 mm plus or minus 2 mm, and mounting material is included. If the leaf is 44 mm, stop. A non-UK reviewer measured about 44 mm between the halves and returned the unit. That measurement is not a UK test. Offer the rings up to the edge before you cut.
The Amazon page has no cutting template, and non-UK notes say the rubber lips can slip off while you fit the rings. Decorative hinged portholes are outside this procedure. UK reviews say the 9 inch clear wall piece is not waterproof.
The HouYeen, the top pick, the GAESHOW, the best value, and the ZONADAH say the screws are not included. A UK HouYeen buyer used M4 countersunk bolts and nuts. Buy those, and check the length against the panel, before you drill. If any answer fails, the circle stays uncut. A certificated door is the refusal on porthole in a fire door. Product choice stays on the porthole buying guide.
A non-fire interior door
The maker's order for the B4000 is plain. Door flat, mark the centre, drill a starter hole, cut with a jigsaw, hang the leaf again, and screw the rings from both sides. Work from the centre you have measured twice. The catalogue for model 0180-0160-A6 gives a 235 mm cut-out and 195 mm of glass for the 250 mm matte aluminium part. That 235 mm figure is the maker's catalogue, not an Amazon bullet. Check it against the rings you unpacked. Cutting 250 mm because the title says 250 mm leaves a hole the flange may not cover.
Support the door so the jigsaw does not splinter the face you will see every day. Cut on the waste side of the line, then trim. Offer both rings and the pane before the last millimetre. The matte VSG pane is the privacy. The listing does not print a BS EN 12600 class, and the pane is not a fire rating. If the lips have walked off the ring, reseat them before you tighten.
Hollow leaves and an opening portlight
A UK account on Workshopshed, from February 2021, is the hollow-door warning. The leaf was hollow, with internal framing, so the bolts needed packing where they crossed a void. If the door sounds hollow, assume a void and a thin skin. A ring screwed only into that skin will pull through. Find the framing, pack the void, or stop and get a joiner.
An opening portlight is a different hole. Do not reuse 235 mm. The HouYeen is about 265 mm outside, the GAESHOW is stated as 10 inch or 26.5 cm, and the ZONADAH is 215 mm. Mark from the flange you have, and drill where the flange is already drilled. Lewmar's torque figure is for Lewmar. There is no torque in these Amazon files. Stop if the plastic flange bends.
One HouYeen shed fit was called watertight after silicone. One buyer could not get a watertight join with the locks kept on the inside, and was left with a gap. If the glass reads as tinted from outside, fit it that way up. Practical Boat Owner's account of a leaking cabin portlight says to bed the joint and not leave the hole open overnight. A bird-hide GAESHOW fit is not a hull.
When the steps stop
Stop when the door is a fire door, when you cannot tell, or when the leaf is uPVC or a security door with a steel skin. Stop for an external door that needs a sealed unit, and for a boat hull or a deck, where a wrong flange leaks into the cabin and the recreational-craft rules may apply. The Masyrt hatch is not fitted by this door sequence. Wall decor is hung.
Call a joiner for a hollow leaf you cannot pack, or for any aperture in a certificated door. Call a yard for a hull. The Consumer Rights Act 2015 is the route if the goods are faulty. It does not repair a hole you cut in the wrong door. If the three checks passed, the MLS order is centre, drill, jigsaw, both rings, door back on. If they did not, the jigsaw stays capped.
Common questions
Do you take the door off?
Yes for an interior door. The maker's order is to lay the door flat, cut, then hang it again and screw from both sides. Cutting a door that is still swinging invites a crooked circle and a blade that grabs. Check the latch and the floor gap when the door goes back.
What diameter do you cut for the MLS unit?
The catalogue for 0180-0160-A6 gives a 235 mm cut-out for the 250 mm matte part, with 195 mm of glass. That number is not printed as an Amazon bullet, so confirm it on the rings in the box before you mark. Do not cut 250 mm just because the title says 250 mm. The portlight diameters are different and must not reuse this figure.
What if the door is hollow?
A 2021 UK workshop fit found a hollow leaf, internal framing, and bolts that needed packing across a void. Knock the door. If it is hollow, find the frame or pack the void before the rings pull the skin in. If you cannot, stop. A solid 40 mm leaf is the case the MLS thickness line is describing.
The portlight arrived without screws. What then?
Buy them before you cut. The HouYeen, GAESHOW and ZONADAH listings say screws are not included. A UK HouYeen review used M4 countersunk bolts and nuts. Match the length to the panel. Do not borrow a torque figure from a Lewmar instruction. That figure is for Lewmar.
Where does silicone get mentioned?
In a UK review of the HouYeen on a shed, where the fit was called watertight after silicone, and in boat-repair writing that beds a leaking portlight and tells you not to leave the hole open overnight. It is not a cure for the decorative portholes. Those are wall pieces, and UK reviews say the 9 inch clear one is not waterproof.
When do you stop and call someone?
When the door might be a fire door, when it is uPVC or an unknown hollow leaf, when the job is a hull or an external sealed unit, or when the rings do not match the thickness. A normal 40 mm interior door that you have checked is the DIY case. Everything else is a joiner, a fire-door specialist, or a yard.
Related pages
Sources
Public UK sources for glazing and craft rules, plus the MLS catalogue for the cut-out. Shelf figures are the amazon.co.uk files used on 19 October 2026. Euro prices in the catalogue are not the UK price.
- Approved Document K, protection from falling, collision and impact (retrieved 19 October 2026)
- Approved Document B, fire safety (retrieved 19 October 2026)
- British Woodworking Federation, machining of apertures (retrieved 19 October 2026)
- BS 8214:2026 commentary on fire-door glazing (retrieved 19 October 2026)
- Recreational Craft Regulations 2017, Schedule 2 (retrieved 19 October 2026)
- GOV.UK guide to the Recreational Craft Regulations 2017 (retrieved 19 October 2026)
- ISO 12216:2020 windows, portlights, hatches and doors (retrieved 19 October 2026)
- MLS catalogue, porthole 0180-0160-A6 (retrieved 19 October 2026)