A bench looks modest in a garden centre and surprisingly large once it's on your patio. It's the most common mistake with outdoor seating: buying the length that felt generous in the shop, then discovering it blocks the route from the back door or leaves nowhere for a side table. Getting the size right isn't difficult, but it does need five minutes with a tape measure before you commit to a design you like.

Here's how to work out what your space can take, and how many people you can seat properly rather than simply squeeze on.

Start with the patio, not the bench

Measure the usable area rather than the whole patio. Slab edges, planting beds, a downpipe, a drain cover, a step down to the lawn — all of these reduce what you can actually use. Note how much wall, fence or railing you could sit a bench against, then subtract anything that interrupts that run.

Walkways matter as much as seating. Allow 60cm as a minimum to pass comfortably, and 75–90cm if someone might be carrying a tray or if it's the main route through the garden. A bench that leaves less than that will have people stepping over it, and the patio will feel cramped even when the bench is empty.

• The length of clear wall or fence available, measured at seat height — a tap, windowsill or downpipe can interrupt it.
• The distance from the back door to the nearest obstacle.
• The width of the main walking route across the patio.
• The position of drain covers, manholes and hose taps.
• Where the sun falls at lunchtime and again in the early evening.

How much seat width does each person need?

As a working rule, allow 55–60cm of seat width per adult. That's the width of the seat itself, between the arms or between the ends of a backless bench. Below that, shoulders start to overlap and nobody settles.

So two people want about 1.2m, three want 1.5–1.8m, and four want roughly 2m or more. Armrests change the sums: a 1.5m bench with arms is realistically a comfortable two-seater with somewhere to rest a book. If you're seating four adults along one side of a table, treat 2m as the target; children need noticeably less.

It's worth matching the numbers to how you actually live. If four people sit down together twice a year, a bench that seats two well will be used far more than one that seats three badly. A bench plus a pair of lightweight chairs often works better than a single long bench, because you can pull the chairs round when the sun moves.

Depth, height and the gaps people forget

Seat height usually falls between 40cm and 45cm, which is deliberately close to a dining chair so the bench can be pulled up to a table. Much lower and older guests struggle to get up; much higher and feet dangle.

Seat depth is typically 45–55cm, but a deep, reclined garden bench can need 65–75cm front to back. That matters if you're fitting it into a narrow strip beside a wall. Then check the clearances around it:

• Behind: leave 5–10cm between the back of the bench and a fence or wall. Air circulation keeps timber and paint in better condition, and it stops the frame rubbing.
• In front at a table: allow 60–75cm to push back and stand up without catching your legs.
• In front on its own: 40–50cm is enough for stretching out.
• Above: check for low windows, pergola beams and hanging baskets before you order something tall.

Match the shape to the space

Straight benches suit long wall runs. Corner benches make the most of an L-shaped patio or an enclosed courtyard, using a corner that wouldn't take a table. Curved benches sit well against round beds and radius edges.

A backless bench in the middle of a patio seats people from both sides, which is handy around a fire pit or a central table — but without a back to lean on, it's a twenty-minute seat rather than an evening one. If you plan to sit out for an hour with a book, a gentle recline beats an upright back every time.

Will you need to move it?

Think about mowing, pressure-washing and clearing the patio for a party. A heavy bench is stable and won't shift in a gale, but you'll need two people and somewhere to put it. A lighter or folding design gives you flexibility in a small space; if it folds away for winter, measure the gap in the shed or under the stairs now rather than in November. Left outside all year, aluminium and hardwood tend to cope with British weather better than softwood — though softwood is perfectly serviceable if you're prepared to treat it regularly.

Stake out the size before you buy

1. Mark the footprint on the patio with masking tape, string or a couple of sheets of newspaper. Include the arms, and the extra depth if the back reclines.
2. Put a dining chair in the middle of the marked area and sit in it for fifteen minutes. Notice whether you keep shuffling sideways looking for elbow room.
3. Walk the route from the back door with something in both hands.
4. Sit there at the time of day you'd really use it. A bench in full afternoon sun is a different proposition from one in shade.
5. Measure the delivery route — gate width, side return, front door, any tight corner. A two-metre bench that won't fit through the gate is no use, however well it suits the patio.

A last check before you order

55–60cm of seat per person. 60cm of walkway as a minimum. A seat height of 40–45cm, with a hand's width left behind the bench.

If your measurements come out tight, seat fewer people or choose a bench without arms. Two comfortable seats that everyone gravitates towards will earn their place on the patio far better than three cramped ones that nobody chooses.

Photo: artemtation / Pixabay