Nursery Pot Sizes Explained: Millimetres, Litres and Gallons

Wholesale lists and plant schedules describe stock by its container, not by the plant: 300 mm, 45 L, tube, or in America 3G. The label says nothing about height or age, or why a species costs three times as much in a 300 mm pot as in a 200 mm one. The idea to hold on to is that pot size is a proxy for time: each step up the ladder is another season of media, water and bench space, and price climbs with it.

This page sets out the Australian ladder from tube to 400 L, with conversions to US gallons and the trade price at each size. It draws on growers' published availability lists as aggregated in the HortOS Plant Price Index, September 2026, and on material from NATSPEC, Greenlife Industry Australia, the Australian Plant Production Standard and Hort Innovation, whose nursery statistics project reports annual production values exceeding $2 billion. It does not claim that any grower's stock matches the heights given, and it does not grade tree stock: that is AS 2303's job, described but not reproduced.

Quick facts

Sizes to 400 mm	By rim diameter: tube, 75, 100, 140, 200, 250, 300 and 400 mm.
Sizes above 400 mm	By litres of media: 25, 45, 75, 100, 200 and 400 L, then ex-ground stock.
US sizes	Classes 1G, 3G, 7G, 15G, 25G and 45G. A US gallon is 3.785 L, but a gallon pot is a class, not a measured gallon.
National median, ex GST	140 mm $7.00, 200 mm $14.00, 300 mm $50.00, 400 mm $110, 45 L $120, 100 L $295, 200 L $650 (HortOS Plant Price Index, September 2026).
Price of patience	Magnolia grandiflora Little Gem: $18 at 200 mm, $1,915 at 400 L, on the same Index.
Conventions	Prices are ex GST, POA means price on application, the Index counts one price per grower, and a list is only as current as its date.

How the Australian ladder works

Growers use two measures on one ladder, with the changeover at about 400 mm: below it a pot is named by rim diameter, above it by litres of media.

• Diameter suits bench stock. Pots to 400 mm are moulded to standard rims and spaced by rim, so the rim number is what everyone counts.
• Volume suits advanced stock. Past 400 mm a container may be a pot, bag or box and grows taller as well as wider, so diameter stops describing root volume. The 400 mm pot and the 25 L or 35 L bag overlap, and one batch may be listed under either name.
• Tubes and liners sit at the bottom. A forestry tube is a square cell about 50 mm across; 75 mm and 100 mm pots are liners, potted on or sold in quantity for revegetation.
• Ex-ground stock sits at the top. Field-grown trees are sold by height, calliper and root ball, in their own transplanting season.

Root volume jumps from 200 mm to 300 mm and again to 400 mm, so price rises far faster than diameter.

Converting between millimetres, litres and gallons

A diameter converts to a volume only approximately, because profiles differ. As rules of thumb, 140 mm holds 1 to 1.5 L, 200 mm 3.5 to 5 L, 300 mm 12 to 15 L and 400 mm 25 to 35 L. Divide litres by 3.785 for US gallons, but on the pot's actual volume, not the class number.

The US ladder runs on container classes written as a number and a G, most often 1G, 3G, 7G, 15G, 25G and 45G. The American Standard for Nursery Stock, ANSI Z60.1, published by AmericanHort, defines each class by a permitted range of volume, so the label is a class name, not a measured gallon. Its ranges are not reproduced here. Match by nearest step: a 200 mm pot lands near 1G, 300 mm near 3G, 400 mm or 25 L near 7G, 45 L near 15G, 100 L near 25G and 200 L near 45G.

The price of patience: what the trade pays at each size

The HortOS Plant Price Index, September 2026 (edition 1, compiled 12 September 2026, 3,526 growers listed, 19,438 plants on current lists) publishes a national median trade price ex GST at each pot size, the middle half, and QLD, NSW and VIC medians. The Index page prints this table.

The median doubles from 140 mm to 200 mm, more than triples to 300 mm, and roughly doubles at each step above; 400 mm and 45 L sit close at $110 and $120, matching the overlap between the names. Each step carries the whole cost of the steps below it plus more care and heavier handling: the buyer pays for the years the grower has already spent. Species ladders from the same Index:

• Little Gem magnolia (Magnolia grandiflora Little Gem): 200 mm $18, 300 mm $55, 400 mm $125, 45 L $155, 100 L $345, 200 L $750, 400 L $1,915. At 300 mm the price page prints NSW $66.84, VIC $49.48 and QLD $60.00.
• Lilly pilly Resilience (Syzygium australe Resilience): 140 mm $8, 200 mm $13, 300 mm $42, 400 mm $109, 45 L $100, 100 L $225, 200 L $508.
• Orange jessamine (Murraya paniculata): 140 mm $7, 200 mm $12, 300 mm $40, 400 mm $85, 45 L $110, 100 L $240.
• Spiny-headed mat rush (Lomandra longifolia): the price page prints tube $1.52, 140 mm $6.20 and 200 mm $11.00; strappy plants for mass planting rarely climb further.

Reading a plant schedule and a grower's list

A schedule that says 300 mm specifies the container and, by convention, a plant grown to fill it: a minimum container size, not a height. One that says 45 L means an advanced plant, usually a tree, in a 45 L container. For more than that, the specifier calls up a standard.

• AS 2303 Tree stock for landscape use is the Australian Standard for assessing tree stock. NATSPEC publishes the guide behind it, Specifying Trees by Ross Clark, described as providing criteria for assessment of all tree stock, benchmarks and calculations, and methods for root development and tree balance, and available as AS 2303. The standard is a paid document, not reproduced here.
• NATSPEC worksections carry the language into contracts: the BUILDING Landscape package includes 0253 Landscape - planting and 0255 Landscape - plant procurement.
• Ex GST applies to every wholesale list price and Index figure; add 10 per cent before comparing with a retail price.
• POA, price on application, appears against advanced stock and large quantities; the price depends on specification, quantity and freight.
• One price per grower is how the Index and its price pages are compiled: one current price per grower for a species at a size, from its trade list, excluding website retail pricing and resellers. Ranges run from the 10th to the 90th percentile once five growers price a size, and 66 per cent of plants on current lists have a single grower, so a species can carry a price without a median.
• NIASA accreditation is separate from size. The Australian Plant Production Standard, home of NIASA, EcoHort and BioSecure HACCP, describes NIASA as accreditation guidelines for NIASA-approved nurseries: production practice, not plant height.
• Freshness is the date on the list. Lists change as stock sells through, so a price from a list months old is a guide, not an offer.

The size ladder at a glance

Volumes, heights and ages are rules of thumb for a typical evergreen shrub or small tree; medians are ex GST from the HortOS Plant Price Index, September 2026. Stock sits outside the ranges because species differ in growth rate, a cultivar grows faster through a Queensland winter than a Victorian one, a plant potted on from 300 mm to 400 mm last month is a 300 mm plant in 400 mm of media, and pruning for form trades height for density.

Species ladders sit on the price pages, a quote can be tested on the price check page, and growers by state are in the grower directory.

What to watch for

• Reading the pot as the plant. A 300 mm label promises a container, not a height; ask for height and potting date.
• Converting the label. Multiplying 15G by 3.785 gives a litre figure no Australian bag matches; convert by nearest step.
• Treating 400 mm and 25 L as different grades. They are often the same stock in a different container; on the Index the 25 L median sits below the 400 mm one.
• Paying for a pot filled last month. Recently potted-on stock has the new size's price and the old size's roots.
• Forgetting freight. Above 45 L, getting a plant off the truck and into the hole can cost as much as the plant, and it is never in the list.

Getting it right

1. Write the schedule in trade terms: species, container size and quantity, with AS 2303 called up for trees.
2. Convert overseas sizes to the nearest Australian step before pricing, and note the conversion on the schedule.
3. Check the median at each size before asking for quotes, then ask each grower for height, potting date and, for trees, AS 2303 assessment.
4. Confirm every price is ex GST, ask what each POA line depends on, get freight and the list date in writing, and inspect advanced stock before it ships.

A word of caution

The medians here are aggregates of growers' published lists on one date, not quotes, and the live price pages update as lists change, so a figure there may differ from the September 2026 edition. Heights and ages are rules of thumb only. For a tree contract, ask the specifier and an AS 2303 assessor; for a species in your region, ask the grower who produces it there.

Sources

• NATSPEC, Specifying Trees: tree stock guide, AS 2303.
• NATSPEC, BUILDING Landscape: planting and procurement worksections.
• Australian Plant Production Standard: NIASA, EcoHort, BioSecure HACCP.
• Greenlife Industry Australia: nursery industry peak body.
• Hort Innovation, Nursery industry statistics 2020-21 to 2024-25: production value survey.
• AmericanHort: publisher of ANSI Z60.1.