The two numbers

Gross area is everything inside the line: the farm boundary for the whole property, or the fence for a paddock. It includes the race down the side, the trees in the corner and the stream through the middle.

Effective area is the part that actually produces feed. It is the number the industry benchmarks use. DairyNZ’s Economic Survey reports results per effective hectare. Beef + Lamb New Zealand’s profitability calculator asks for effective hectares. It says to leave out unusable land such as swamps, lakes, rivers and reserves, ungrazed areas such as forest blocks, and land used for something other than farming, such as horticulture. Wide-spaced trees that are regularly grazed underneath stay in.

What usually comes out

Races, lanes and tracks
Yards, sheds, houses, effluent ponds and other built areas
Bush blocks, plantations and shelterbelts that stock don’t graze
Fenced-off streams, wetlands and riparian margins
Retired or covenanted land
Land used for something else, such as a gravel pit or orchard
Steep faces or scrub that stock don’t actually use

The judgement calls

Not every deduction is obvious, which is why two people can measure the same farm and get different effective areas. The ones worth agreeing on:

Grazed trees. Wide-spaced trees with pasture underneath that stock graze stay in.
Occasional faces. A face stock graze now and then is a judgement call. Decide once and apply it consistently.
Crops, silage and hay. These paddocks still grow feed, so they normally stay effective.
Small drains and gullies. A narrow unfenced drain inside a grazed paddock is usually too small to matter. A fenced strip that stock can’t reach is not.

A simple test: if stock graze it, or it grows feed for them, it’s effective. Whatever the rules, write each deduction down so the number can be checked and argued with.

A worked example

An illustrative paddock of 12.00 ha gross:

Item	Hectares
Gross area inside the fence	12.00
Less: Race along the northern fence	−0.35
Less: Fenced-off stream margin	−0.42
Less: Pine shelterbelt, not grazed	−0.18
Less: Gorse face stock don’t use	−0.55
Effective area	10.50

That’s 1.50 ha, or 13% of the paddock, that doesn’t grow feed. Two ways it shows up:

Fertiliser. At 250 kg of product per hectare, an order worked out on gross area is 3,000 kg. On effective area it’s 2,625 kg. That is 375 kg more than the grazed part of this one paddock needs, and wherever it goes on, it isn’t growing grass for stock.
Stocking rate. The same mob on 10.50 effective hectares is a stocking rate about 14% higher than the gross figure suggests. Feed budgets built on gross area overstate the feed you have.

Which number for which job

Job	Use
Feed budgets and pasture cover per hectare	Effective
Stocking rate and industry benchmarking	Effective
Fertiliser and spray orders	Effective, or the area actually spread
Fencing, and the overall size of the property	Gross
Selling, buying or leasing a farm	Both. Expect to be asked for each

Why the area you’ve always used may be wrong

Paddock sizes get handed down. Fences move, races get widened, and a corner gets planted, but the number in the notebook stays the same. The title area isn’t a shortcut either: it describes the legal parcel, and fences are not always on the boundary. In rural areas the title lines you see on online maps can also be tens of metres out. See do you need a surveyor or a farm mapper?

How we measure it

Every Baseline Mapping package gives you gross area for each paddock. Baseline Plus ($1,250 + GST) adds effective area for every paddock, with each deduction itemised and agreed with you, so you can see exactly what came out and why. See what’s in Baseline Plus.

Gross area or effective area: which number should you use?