Walk into any plywood section and you'll see a wall of sheets that all sort of look the same from a distance: different thicknesses, different finishes, different price tags, and no obvious clue about which one actually suits what you're building. It's one of the most common questions we get from tradies and weekend builders alike: "which plywood do I actually need?" So here's a straightforward breakdown to help you pick the right sheet the first time, instead of guessing and hoping.

Start with the job, not the timber

Before you even look at grades or thicknesses, get clear on what the plywood needs to do. Is it structural, holding weight, spanning a gap, forming part of a wall or floor? Is it decorative- something that'll be seen, stained, or painted? Or is it going somewhere wet outdoors, near a pool, or below the waterline on a boat? The answer changes everything else on this list.

Structural work (flooring, bracing, subfloors, formwork) needs plywood rated for load-bearing use, usually structural plywood graded to Australian Standards.

Decorative or furniture work (cabinetry, shelving, feature walls) calls for a plywood with a clean, sanded face, often hoop pine or a decorative-grade sheet with minimal visible patching.

Wet or exterior applications (boat building, outdoor furniture, marine environments) need marine plywood, which is manufactured with waterproof glue bonds and fewer internal voids so it holds up under repeated moisture exposure.

Getting this first decision right saves you from either overpaying for structural-grade timber on a job that didn't need it, or under-specifying a sheet that swells and delaminates within a season.

Thickness matters more than people expect

Plywood generally comes in sheets ranging from around 3mm right through to 25mm, and the thickness you need depends entirely on span and load.

• 3–6mm sheets suit lightweight panelling, drawer bases, and craft or hobby projects.

• 9–12mm is a common middle ground for shelving, wall lining, and light furniture work.

• 15–18mm is the range most flooring and general structural jobs sit in.

• 19–25mm comes into play for heavier structural applications, benchtops, or anywhere the sheet needs to span further without flexing underfoot.

If you're unsure, it's worth erring slightly thicker for anything load-bearing  a floor that flexes is far more annoying to fix after installation than it is to prevent beforehand.

Know your grades

Plywood is graded by the quality of its face veneers, and this is where a lot of people get caught out buying a lower grade than they actually need (or paying extra for a finish they'll never see).

A/B or A/C grades give you at least one clean, near-defect-free face  worth it if the sheet will be visible or painted. Lower grades like C/D are perfectly fine for structural or hidden applications like subfloors and formwork, where nobody's ever going to look at the surface again. There's no point paying for a furniture-grade face on plywood that's going under a house.

Don't skip the environment test

One more question worth asking before you buy: where will this sheet actually live once installed? Indoors and dry, it opens up almost every plywood type. Anywhere exposed to weather, humidity, or ground moisture  decking substrates, external cladding, boat interiors really only leaves you with marine or exterior-rated plywood as a sensible option. Standard interior plywood in an outdoor setting is a false economy; it'll usually need replacing well before a correctly rated sheet would.

A quick way to narrow it down

If you're still not sure which sheet fits your project, run through these three questions:

1. Is it structural, decorative, or exposed to moisture?

2. What span or load does it need to handle, and does that push you toward a thicker sheet?

3. Will the surface be visible, or is it going somewhere hidden?

Answer those three and you'll usually land on the right category of plywood before you've even looked at a price list.

Buying plywood online in Melbourne

If you're still weighing up options, it's worth having a chat with a supplier who can match the sheet to the job rather than just the budget. We stock a full range of structural plywood, marine plywood, decorative sheets, and OSB with sheet sizes and thicknesses to suit everything from a quick shelving job to full structural fit-outs, delivered across Melbourne or ready for pickup.

Browse the full range of plywood online, or get in touch if you'd rather talk through the specifics of your project before you order.