Hexagon, Round or Rectangle? Choosing a Shape for Your DIY Hot Tub

Hot tub shapes are one of the first things people ask me about when they start sketching a DIY build. Square or rectangle? Round? Something a bit different, like a hexagon or an octagon? The shape changes far more than the look. It affects how many people fit, how much water you heat, how you build the walls, how you lay the tiles, how the plumbing runs and what the cover costs.

Here’s how the main shapes compare, what each one is really like to build, and which I’d pick for which job.

The short version

• Square or rectangle is the easiest and cheapest to build, tile and cover. It’s my first choice for most DIY builds, and it’s what most of my plans are drawn as.
• Round is the most sociable, with everyone facing the middle, but curved walls are the hardest to build well and the cover is made to measure.
• Hexagon and octagon are the middle ground: a round feel with straight walls, so you get the look without forming curves. The corners take more cutting and the cover is still made to measure.
• Freeform and L-shapes look great in the right garden but cost more at every stage. Get a design drawn before you dig.

Hot tub shapes compared

To make a fair comparison, picture each shape fitting inside the same 8ft x 8ft (2.44m x 2.44m) box, measured across the flats for the hexagon and octagon. The square uses all of it. Every other shape gives some of that space back to the patio.

Shape (fits an 8ft / 2.44m box)	Water surface area	% of the square	Build difficulty	Cover
Square	64 sq ft (5.95 m²)	100%	Easiest	Standard size, widely available
Hexagon	55 sq ft (5.15 m²)	about 87%	Moderate: six angled corners	Made to measure
Octagon	53 sq ft (4.93 m²)	about 83%	Moderate: eight angled corners	Made to measure, but a common shape
Round	50 sq ft (4.68 m²)	about 79%	Hardest: curved walls	Made to measure, but a common shape

Less surface area means less water at the same depth, so a round or hexagon tub is a little cheaper to fill and heat than a square tub of the same width. It also means less bench, so fewer people. As a rough rule I allow about 24in (60cm) of bench per adult, but where the corners fall matters as much as the total length.

Square and rectangle: the practical choice

There’s a reason most DIY hot tubs are square or rectangular, and why most of my hot tub plans are drawn that way. Every stage is simpler.

Why it’s easier to build

• Walls: blocks, bricks and ICF all come with square corners. You set out a rectangle with a tape and the 3-4-5 rule, and you’re away. My guide to hot tub wall construction compares block, CMU, ICF and poured concrete.
• Seats and loungers: straight benches are easy to form, and the corners make natural spots for a corner seat or a lounger like The Kyle.
• Tiles: you can use larger-format tiles on flat walls, with fewer cuts.
• Cover: square and rectangular covers are the standard product, so you have more choice and shorter lead times.

The downsides

The main one is that people sit along the walls in lines rather than facing each other, so a long, narrow rectangle can feel less sociable than a round tub. Corners can also become dead space if you don’t design a seat into them. Getting the shape close to square (8×8, 7×7, 10×10) helps, which is one reason the 8ft x 8ft plans are my best seller.

Round hot tubs: sociable, but harder work

A round tub is lovely to sit in. Everyone faces the middle, there are no corners, and the water flows round evenly. In a concrete or block build, though, the curve has to come from somewhere.

How you build a round concrete hot tub

• Poured concrete with curved formwork (flexible plywood or hardboard sheets, braced well). It works, but curved formwork takes time.
• Sprayed concrete (shotcrete or gunite), which is how most curved pools are built. It’s normally a contractor job.
• Small blocks or bricks laid to a radius. The tighter the curve, the smaller the unit needs to be, and the more render you need to smooth out the facets.
• ICF cut and braced to a curve. Possible, but fiddly. Check what your ICF manufacturer recommends before you plan on it.

Whichever way you go, the walls must be properly reinforced and the structure designed for the load of the water and the soil around it. If you’re not sure, get a structural engineer to check the design.

Tiling, plumbing and covers

Curves need small mosaic tiles, usually on a mesh backing, so they follow the wall without lipping. Bench seats have to be formed to the same curve. Every plumbing fitting sits on a curved face, so take care setting each one square to the wall. Covers are made to measure, though round is a common shape and not hugely more than a square one.

Hexagon hot tubs: the round feel with straight walls

A hexagon hot tub is a good compromise. You get the sociable, face-the-middle layout of a round tub, but every wall is flat. That means flat tiling, flat bench seats and straight runs of block.

What’s harder about a hexagon

• The corners. Each inside corner of a regular hexagon is 120°, not 90°. With block or brick, that means cutting and mitring every course at six corners, and getting the setting-out exactly right from the first course. With ICF, standard corner blocks are usually 90° or 45°, so a hexagon generally means custom cuts and extra bracing.
• The setting-out. Mark the centre, then set out the six points at equal distances. Small errors in the first course become big ones by the top.
• The seats and the cover. Bench seats meet at angles, so each corner needs a little thought. The cover is made to measure.

Niels’s hexagon build

The best example I have is Niels’s DIY hexagon hot tub in the Netherlands. I designed the tub and the plumbing, and he’s built it in stages: insulated base, block walls, a dark grey tiled shell and bench seats stepping down to a hexagonal footwell. Every jet position was on the drawing before a single tile went on.

Octagons: easier corners than a hexagon

An octagon has eight sides and 135° inside corners, so it looks even closer to round. The handy part is that each corner is a 45° turn, which is a much more common angle for cutting and for ICF corner pieces than the 60° turn a hexagon needs. Marshall’s octagon hot tub in California went a different way, with poured concrete walls, and it’s a good example of how an angled shape comes together with a proper plumbing layout.

Freeform, L-shapes and combos

Freeform, lagoon-style and L-shaped tubs can look stunning, especially wrapped around a corner of a patio or built next to a pool. They’re also the hardest to build, plumb evenly and cover. If that’s what you want, have it designed first rather than working it out on site. I go into more of the layout side in in-ground hot tub designs.

How the shape affects the cost

Shape alone rarely doubles a budget, but it adds up across the build:

• Time: angled corners and curves mean more cutting, formwork and setting-out.
• Tiles: mosaic on curves costs more to buy and to fix than larger tiles on flat walls.
• Cover: going by retailer price guides in October 2026, a standard square cover is roughly $350–550 in the US, round or octagonal around $400–600, and fully custom shapes $500–900 or more. In the UK, made-to-measure covers up to 2.4m (about 8ft) start at around £375. Prices vary by region, size, foam thickness and supplier, so get quotes for your exact tub.
• Water and heating: a smaller surface area means slightly less water to heat, which helps the round and angled shapes a little.

Which hot tub shape should you choose?

• First build, tight budget or a tight space: square or rectangle. It’s simpler at every stage, and the plans, covers and parts are all standard.
• You want everyone facing each other: a hexagon or octagon gives you most of that with straight walls. Round if you’re happy with curved formwork or bringing in a sprayed-concrete contractor.
• A feature tub that’s the centrepiece of the garden: hexagon, octagon or round, with the design and plumbing drawn properly before you dig.
• Fitting into a corner or alongside a pool: a rectangle or L-shape, again designed first.

Whatever the shape, the depth, seat heights and footwell matter just as much for comfort. The plumbing, electrics and structure are the same story whatever the outline: any electrical work, bonding and earthing must be done by a qualified electrician to your local regulations, and anything structural should be checked by an engineer.

If a standard size suits you, my CAD-drawn hot tub plans come in 21 sizes with the plumbing layout, parts list and instructions. If you want a hexagon, octagon, round or something of your own, my custom design consultancy is how Niels’s hexagon started, or you can sketch your shape in Tub & Pool Designer Pro and have me turn it into architectural CAD and a plumbing design.

FAQs

What is the best shape for a hot tub?

For most DIY builds, square or rectangular. It’s the easiest to build, tile and cover, and it uses the space best. Round, hexagon and octagon tubs are more sociable but take more work.

Is a hexagon hot tub hard to build?

It’s harder than a square but easier than round. The walls are straight, but every corner is 120°, so blocks need cutting and mitring, and the setting-out has to be accurate from the first course. The cover is made to measure.

Can you build a round concrete hot tub yourself?

Yes, with curved formwork for poured concrete or small blocks laid to a radius and rendered. Sprayed concrete is usually a contractor job. Use mosaic tiles on the curves, and have the structure checked by an engineer if you’re unsure.

Do round or hexagon hot tubs hold less water?

Yes, if they fit in the same width as a square tub. In an 8ft (2.44m) box, a round tub has about 79% of the square’s surface area and a hexagon about 87%, so less water to fill and heat, but less seating too.

Are covers for round and hexagon hot tubs more expensive?

Usually a little. Round and octagonal covers are common shapes and cost only slightly more than square ones. Hexagons and freeform shapes are made to measure and cost more. Get a quote for your exact tub before you commit to a shape.

What shape are you planning? Tell me in the comments below.

Cheers,
Andi