How Big Is the Hole in Your House?
Your blower door test came back as a number. This calculator turns that number into something you can actually picture — the size of the hole in your building envelope.
Your blower door test came back at 5 ACH50. Or 9. Or 0.7. But what does that actually mean? A number on a report is hard to feel. A hole in the wall is not.
This calculator converts your air leakage result into equivalent leakage area — the size of a single hole that would leak the same amount of air as every crack and gap in your home added together. It shows that hole in cm², as a round hole you can measure with a ruler, and next to everyday objects so you can picture the scale.
It pairs with our ACH50 calculator: that one answers “is my result good?” — this one answers “what does my result physically mean?”
Your equivalent hole size
Enter your ACH50 result (or your raw blower door airflow) along with your home’s dimensions. The defaults represent a typical 200 m² Adelaide home at NCC better-practice airtightness — adjust the sliders to see how the hole grows and shrinks.
Hole Size Calculator
Turn your blower door result into a hole you can picture — the single opening that would leak the same amount of air at the 50 Pa test pressure.
Equivalent hole in your building fabric
1,347 cm²
that’s 0.135 m² — a round hole about 41 cm across
At 5.0 ACH50, your home has an equivalent leakage area of approximately 0.13 m² when tested at 50 Pa. In reality this leakage is spread across hundreds of cracks, gaps and penetrations throughout the building rather than one large opening.
Closest comparison
dinner plate-sized
a dinner plate ≈ ~27 cm across
This is the Equivalent Leakage Area at the 50 Pa test pressure — not a normal, everyday open hole. The 50 Pa test pushes far harder than real conditions, so it’s a like-for-like comparison for visualisation, not the size of gap you’d feel day to day.
What this means
Better than average, but still has measurable leakage. There is room to improve comfort and energy use with targeted sealing.
At this leakage rate, the entire air volume of your home could be replaced every 12 minutes during a blower door test.
Closest comparison: dinner plate
How does this compare?
Your result: 5.0 ACH50 — Good Modern Home
Equivalent leakage area at 50 Pa, modelled as a sharp-edged orifice (Cd 0.61, air density 1.2 kg/m³). Real leakage is spread across hundreds of cracks and gaps, not one perfect hole — this is an illustration, not a measurement.
What is “equivalent leakage area”?
A blower door test mounts a calibrated fan in a doorway and holds the house at a steady pressure — by convention, 50 Pascals, roughly the push of a 32 km/h wind hitting every wall at once. The fan measures how much air it has to move to maintain that pressure. That airflow, in cubic metres per hour, is your raw result.
Airflow on its own is abstract. So we ask a different question: if all the leakage in the building came through one clean hole instead of being spread across hundreds of cracks, how big would that hole have to be to leak the same amount of air at the same pressure? That single, imaginary opening is the equivalent leakage area.
The formula
A = Q ÷ ( Cd × √(2 × ΔP ÷ ρ) )
A = leakage area · Q = airflow (m³/s) · ΔP = 50 Pa · ρ = 1.2 kg/m³ · Cd = 0.61
Round hole diameter = √(4A ÷ π)
The leakage is treated as a sharp-edged orifice — the standard engineering model for flow through an opening. The discharge coefficient (Cd ≈ 0.61) and air density (ρ ≈ 1.2 kg/m³) are the usual values for this kind of calculation at room conditions.
What the hole looks like at each airtightness level
These figures are for a typical 200 m² single-storey home with 2.7 m ceilings — a building volume of 540 m³. The equivalent hole is the opening at the 50 Pa test pressure.
| ACH50 | Benchmark | Equivalent hole | Looks like |
|---|---|---|---|
| 0.6 | Passive House | ~160 cm² · 14 cm wide | A grapefruit |
| 2.1 | High performance | ~570 cm² · 27 cm wide | A dinner plate |
| 5 | NCC better practice | ~1,350 cm² · 41 cm wide | Bigger than a dinner plate |
| 9.4 | Average new build | ~2,530 cm² · 57 cm wide | Approaching an open window |
| 15–20 | Average Aussie home | ~4,000–5,400 cm² · 72–83 cm wide | An open window |
The jump is bigger than most people expect. Moving from an average new build to high-performance airtightness is the difference between leaving a window open and leaving a dinner plate’s worth of gap — a roughly four-to-five-fold reduction in the hole.
One important caveat. The equivalent hole is a way to picture the leakage — not a real hole you can find and patch. Your home doesn’t have one big opening; it has hundreds of small ones spread across junctions, penetrations and edges. Adding them together into a single hole makes the scale visible, but the fix is always many small details, not one repair.
The figure is also calculated at the 50 Pa test pressure, which is much stronger than everyday conditions. Under normal wind and temperature the effective opening is smaller — but the 50 Pa number is the honest, assumption-free way to compare one home to another straight from the test.
Where the hole actually comes from
If the leakage isn’t one hole, where is it? In Australian new construction the equivalent area is usually made up of these paths, each contributing a slice of the total:
Ceiling / roof junction
The most common single source — where the ceiling plane meets the top plate and roof space.
Service penetrations
Every cable, pipe and conduit through the envelope is a leak if it isn't carefully sealed.
Window & door perimeters
Frames that aren't taped or sealed to the structure leak, especially at the corners.
Downlight recesses
Recessed fittings open straight into the ceiling cavity — a notorious leakage path.
Exhaust & range hood ducts
Penetrations for fans and range hoods need careful detailing to keep the airtight layer continuous.
Slab perimeter
The junction between slab, frame and floor covering is often left unsealed in single-storey homes.
ACH50 Calculator
Is your blower door result good? Calculate ACH50 and compare it to NCC, MVHR and Passive House benchmarks.
Airtightness Explained
What airtightness means and how it’s achieved in construction
Blower Door Testing
HiPer Haus blower door testing across Adelaide and South Australia
Range Hood Makeup Air Calculator
Will your range hood suck air through your walls? Estimate the negative pressure and makeup air needed
What Is MVHR?
How mechanical ventilation with heat recovery works — and why airtightness matters for it
Frequently asked questions
What is equivalent leakage area?
Equivalent leakage area (ELA) is the size of a single, clean hole that would leak the same amount of air as all the scattered cracks and gaps in your building envelope combined. Your blower door test measures total airflow at a set pressure; ELA converts that airflow into one imaginary opening so you can picture the scale of the leakage. It is an illustration, not a physical hole you could find and patch.
How is the hole size calculated from a blower door result?
The leakage is modelled as a sharp-edged orifice using the standard flow equation Q = Cd · A · √(2·ΔP / ρ), rearranged to solve for area A. Q is the measured airflow in cubic metres per second, ΔP is the 50 Pascal test pressure, ρ is air density (about 1.2 kg/m³), and Cd is the orifice discharge coefficient (about 0.61). Dividing the resulting area by π and taking the square root of four times it gives the diameter of the equivalent round hole.
Why is the hole so big at 50 Pa?
The blower door test runs at 50 Pascals — roughly the pressure of a 32 km/h wind pushing on every surface of the house at once. That is far stronger than everyday conditions, so the equivalent hole at 50 Pa looks large. Under normal pressures the effective opening is smaller. The 50 Pa figure is still useful because it is tied directly to the test, with no extra assumptions, and it makes the relative difference between a leaky and an airtight home easy to picture.
Is the equivalent hole a real hole I can find and seal?
No. Real air leakage is distributed across hundreds of small paths — the ceiling-to-wall junction, service penetrations, window perimeters, downlights, the slab edge and more. There is no single hole to plug. The equivalent leakage area simply adds all of those paths together into one number you can visualise. Sealing happens across many small details, which is why a mid-construction blower door test with smoke is so valuable for locating them.
How does hole size relate to ACH50?
ACH50 tells you how airtight your home is relative to its size; hole size tells you the physical scale of that leakage. They come from the same test. A 200 m² home with 2.7 m ceilings (540 m³) at 5 ACH50 leaks about 2,700 m³/h, which is an equivalent hole of roughly 1,350 cm² at 50 Pa — bigger than a dinner plate. The same home at Passive House 0.6 ACH50 leaks about a grapefruit-sized hole. Use the ACH calculator to judge whether your number is good, and this one to picture what it means.
A number is easy to ignore. A hole is not.
Picturing your leakage as an open window is what makes airtightness feel worth doing. The good news: the hole shrinks fast with careful detailing and a mid-construction test to find where the air is getting through — long before the linings go on.
Want to shrink the hole?
HiPer Haus carries out blower door testing across Adelaide and South Australia — mid-construction and at completion. We find the leakage paths, explain what your result means, and advise on targeted sealing to bring the number down.