Check the building line before relying on recorded land area
Two parcels recorded as 300 m² can provide different site-area denominators for a new building.
A narrow alley, a corner cut or a planning-facility exclusion can reduce the area used to calculate coverage and floor area ratio, even though the sale listing still refers to the cadastral area.
Discovering these deductions after purchasing an older house or vacant site can require a smaller design and a revised purchase budget.
This tool estimates required road width, road setbacks and eligible corner cuts under Korean rules.
It then compares effective site area, ratio-based size ceilings, effective purchase price per pyeong and a budget based on your own target unit cost.
An heir considering development can use the same review to prepare clear questions for the local building authority and an architect.
Korea-specific scope and datesThe Korean 2026 rules were verified on 2026-10-20.
Reference dates are limited to 2026-10-06 through 2026-12-31, starting with the current Decree’s effective date and assuming these rules remain unchanged.
Effective area is a Building Act denominator reference, not an ownership-area determination or an approved building design.
Prepare four groups of inputs and their evidence
Site and roads
Prepare recorded site area, currently secured road width, the road-facing parcel boundary length and secured contact after building-line review.
Check legal designation, motor-only restrictions, dead-end status and obstacles opposite the site.
Do not assume the paved width in a photograph equals the legally designated road width.
Exclusions and layout
Identify setback strips, corner geometry and any additional facility exclusion.
For irregular parcels, two setbacks or overlapping regions, use the measured union of all exclusions from a survey or design drawing.
A separately designated building-line distance is recorded without automatically reducing the denominator.
Planned scale
Enter the coverage and FAR actually applicable to the site and use under local rules.
Planned FAR-counted floor area differs from total floor area including basement and other excluded floors.
Entering a percentage does not establish its legal applicability to your parcel.
Prices and reference date
Enter the purchase price and your acceptable price per effective pyeong.
Each evidence group can be unknown, assumed or confirmed; confirmed inputs need a reference date and evidence memo.
Blank is not zero: use 0 only for an established absence of an exclusion or cost.
The numeric fields accept comma-separated input and up to six decimal places.
Tool limits are 1,000,000 m² for site area, 10,000 m for lengths, 100% for coverage and 1,500% for FAR.
These are input limits, not legal percentage allowances.
The initial form is blank; fictional examples are available to demonstrate the calculation.
Required widths for standard and dead-end roads
Building Act Article 2(1)(11) addresses both the general road width and the notice/designation requirements for a legal road.
A path used by pedestrians does not automatically qualify.
Decree Article 3-3 provides separate width rules for dead ends and for sections designated and published by the authority because terrain makes a vehicle road difficult to install.
Required road widths by type and complete dead-end length| Road condition | Required width | Check |
|---|
| Standard road | 4 m | Legal designation or notice |
| Dead end shorter than 10 m | 2 m | Whole-road start/end points |
| Dead end from 10 m to below 35 m | 3 m | Exactly 10 m is included |
| Dead end at least 35 m long | 6 m | 4 m in nonurban eup/myeon areas |
| Designated terrain exception | 3 m | 2 m for a dead end below 10 m |
The 4 m exception for a dead end at least 35 m long specifically requires an eup or myeon area outside an urban area.
An undeveloped appearance or nonurban classification alone is insufficient.
The terrain exception likewise requires the authority’s designation and publication rather than the user’s assessment that the road is steep.
Shared widening and an obstacle on the opposite side
Building Act Article 46(1) establishes the building line when a road is narrower than its required width.
The following distances and strip areas are simple geometry references for a straight boundary parallel to a road of uniform width.
A changing width, kinked boundary or overlap with another excluded region needs a drawing-based review.
Ordinary shared-width condition
d = max(0, (W − w) / 2)
W is required width; w is current width.
With W=4 m and w=3 m, the reference setback on this site is 0.5 m.
For a 20 m boundary, the isolated strip is 10 m².
Opposite slope, river, railway or similar obstacle
d = max(0, W − w)
Where the statutory obstacle condition applies, review a line securing the required width from the opposite road boundary.
The same 4 m/3 m inputs give a 1 m setback and a 20 m² strip along a 20 m boundary.
The reference setback is zero once current width reaches required width.
That does not establish the absence of a separately designated line or other layout constraint.
A calculated widening does not prove completed road construction or secured access rights; the access test continues to use the currently secured width.
Corner cuts depend on both widths and the intersection angle
Decree Article 31(1) connects two points measured back along the road boundaries at a corner of roads narrower than 8 m.
Its table considers the width of each road and the intersecting road.
Use the site-side interior angle between the boundary lines, rather than a vehicle’s turning angle or the exterior supplementary angle.
Two corner-cut distances by road-width combination and site-side angle| Road widths A / B | Below 90° A / B | 90° to below 120° A / B |
|---|
| 6 to below 8 m / 6 to below 8 m | 4 m / 4 m | 3 m / 3 m |
| 4 to below 6 m / 6 to below 8 m | 3 m / 3 m | 2 m / 2 m |
| 4 to below 6 m / 4 to below 6 m | 2 m / 2 m | 2 m / 2 m |
Isolated corner triangle = a × b × sin(θ) / 2
a and b are the two distances along the road boundaries.
For 4 m/6 m roads meeting at 90°, 2×2×sin(90°)/2 gives 2 m².
At 89.999°, the distances change to 3 m/3 m and the area is approximately 4.5 m².
For 6 m/6 m roads at 60°, the distances are 4 m/4 m and the area is approximately 6.928203 m².
At an angle of 120° or above, or where either road is at least 8 m wide, the automatic corner cut under this table does not apply.
An individual designation or another drawing constraint may still exist.
If one road is below 4 m and the remaining angle/width conditions are otherwise in scope, the table does not supply a distance: the tool requests a surveyed union rather than inventing zero area or a 2 m cut.
Use the exclusion union and distinguish separate building lines
Decree Article 119(1)(1)(a) addresses the site between a road and a building line under the proviso to Article 46(1).
Paragraph (b) addresses qualifying city/county planning-facility areas.
It contains an exception for facility sites where buildings or structures are installed under National Land Planning Act Article 47(7); do not deduct every facility overlap without checking its treatment.
Automatic estimate
Use one straight uniform strip, or one corner with no road setback.
Additional facility area must already have overlaps with road and corner areas removed.
Two road setback strips, or any corner combined with a road setback, leave automatic effective area pending to prevent double counting.
Surveyed total union
Enter all road, corner and facility exclusions as one measured union, counting each place once.
The additional facility field and isolated geometry rows are not added again in this mode.
Use a drawing where a cut extends beyond a parcel boundary or its boundary distances do not fit the available frontage.
A separately designated Article 46(2) building line can be established in an urban area within the Decree Article 31(2) limit of 4 m.
Its distance is retained as layout information and is not automatically deducted from the effective denominator.
Do not treat an open-space requirement or district-plan building limit as the same statutory deduction merely because it is expressed as a setback distance.
Article 47 restrictions at the building line also require separate design review.
Effective area, ratio ceilings and the target-price budget
- Effective site area = recorded site area − exclusion union counted once
- Coverage-based footprint ceiling = effective site area × coverage / 100
- FAR-counted floor-area ceiling = effective site area × FAR / 100
- Effective cost per pyeong = purchase price / (effective area / 3.3058)
- Budget at your target unit cost = target effective price per pyeong × (effective area / 3.3058)
A ratio ceiling does not describe the actual footprint shape that can fit on the parcel or establish the final number of storeys.
Parking, daylight, height, landscaping and open spaces may reduce the design further.
FAR-counted floor area also differs from total building floor area: review the Article 119(1)(4) treatment of basements, accessory above-ground parking and other excluded areas on the drawings.
The conversion is one pyeong = 3.3058 m², consistent with the existing real-estate area calculator.
Money is displayed to whole KRW and area to at most six decimal places, while comparisons use values before display rounding.
A zero target-budget excess means the entered purchase price is within your own target; it does not establish that the land is undervalued in the market.
Worked examples for a fictional 300 m² parcel
Fictional site-area deductions and resulting coverage/FAR ceilings| Fictional condition | Excluded m² | Effective m² | 60% footprint m² | 200% FAR m² |
|---|
| Recorded-area comparison | 0 | 300 | 180 | 600 |
| 3 m standard road, 20 m boundary, shared widening | 10 | 290 | 174 | 580 |
| Same dimensions, opposite obstacle | 20 | 280 | 168 | 560 |
| 4 m/6 m roads, 90° corner only | 2 | 298 | 178.8 | 596 |
At a purchase price of KRW 600,000,000 in the straight-road example, the recorded cost is KRW 6,611,600 per pyeong and the effective cost is about KRW 6,839,586 per pyeong.
A target of KRW 6,000,000 per effective pyeong produces a budget of about KRW 526,347,631 and a price excess of about KRW 73,652,369.
This compares the same price against a smaller denominator; it does not establish an actual loss in market value.
Inputs loaded from a fictional example keep that provenance in the exported review after editing.
Ordinary 2 m contact and enhanced 6 m-road/4 m-contact rules
Building Act Article 44 generally requires at least 2 m of contact with a road and excludes roads used only by motor vehicles.
Exceptions involving recognized unimpeded access, authority-recognized open spaces or farm huts need separate review.
Decree Article 28(2) requires at least 4 m of contact with a road at least 6 m wide when total floor area reaches 2,000 m² for a general building or 3,000 m² for a factory.
Thresholds and separate-road checks
- A general building at 1,999.999 m² and one at 2,000 m² fall on different sides of the enhanced threshold.
- The factory threshold is 3,000 m², not 2,000 m².
- Livestock buildings, crop-growing buildings and other possible ordinance exceptions remain pending in special-review mode.
- Do not combine two separate short road contacts to manufacture 4 m of frontage.
- A road expected to become 6 m wide after a setback is not automatically treated as currently secured at 6 m.
The straight-road example can therefore produce a 290 m² effective site estimate while current-width access remains numerically short.
Area estimation and road securing are separate decisions.
Confirm usable contact after the building line is established; the tool does not automatically subtract a corner distance from frontage or assume a longer contact.
Step-by-step use before a purchase contract
- Collect the cadastral plan, land-use confirmation and road designation/public notice, then set the reference date and evidence states.
- Distinguish whole-road length, parcel boundary length and secured road contact, and enter each currently secured road width.
- Use automatic estimation only for supported simple shapes; switch to the surveyed union for overlapping road/corner/facility exclusions or an irregular parcel.
- Enter checked coverage/FAR, planned FAR-counted area, total floor area and use; examine area losses and road-access shortfalls separately.
- Enter purchase price and your target effective unit cost, then save the TXT review and evidence checklist for the authority or architect.
Before buying an older house
An existing building does not establish that a replacement of the same size is allowed.
Confirm road designation, the line applicable to rebuilding, current ordinances and parking layout before fixing the land budget and paying design fees.
Developing inherited land
Check title and recorded area, then examine physical access and development constraints separately.
Ask the architect for both total floor area and FAR-counted area, and supply the surveyed exclusion drawing to reduce repeated assumptions.
Saved and printed reviews include inputs, evidence states, date, memo, fictional-example provenance and completed checklist items.
The memo is printed as plain text; parcel details and prices are not attached to action analytics.
After changing an evidence state, save a new review so the updated assumptions are clear.
Frequently asked questions
Does a 3 m road always mean a 0.5 m setback?
Only in the simple standard-road case with a 4 m required width and shared widening on both sides.
Dead-end rules, a slope, river or railway on the opposite side, road designation and an already established building line can change the answer.
A photograph of the paved width does not establish the legal boundary.
When is the corner cut exactly 2 m²?
At a 90° site-side angle with two 2 m distances along the road boundaries, the triangle is 2 m².
Distances can change below 90° or when both roads are at least 6 m wide.
Do not add an isolated triangle a second time where it overlaps a setback strip.
Is dead-end length just the section in front of my land?
No.
Use the entire applicable dead-end road length.
Your parcel boundary length, road width and secured contact length are separate measurements.
Ask the authority to confirm the start/end points and the extent of any designated terrain exception.
Is a separately designated building line deducted from site area?
An Article 46(2) designation is distinguished from the road/corner setback in the proviso to Article 46(1).
This calculator records its distance as a layout constraint without automatically deducting it from the denominator.
Check the actual designation and any independent statutory exclusion.
Are basement floors excluded from both FAR and enhanced road access?
The tests serve different purposes.
Decree Article 119(1)(4) governs FAR-counted exclusions, while Article 28(2) uses total floor area.
Enter the two floor-area figures separately.
Compare the general-building 2,000 m² or factory 3,000 m² threshold using total floor area.
Does a setback automatically transfer my land to the road owner?
Effective site area is a Building Act calculation reference.
It does not determine parcel subdivision, land-category changes, ownership transfer, incorporation into a road or compensation.
Check the cadastral and title records and the authority’s position separately.
What happens if the exclusion equals or exceeds my site area?
An equal exclusion produces zero effective area and an undefined effective price per pyeong, shown as pending.
An exclusion greater than the recorded site produces an error rather than silently forcing the answer to zero.
Check units, duplicate areas and confusion between boundary length and total road length.
Can I buy if the budget and access numbers look acceptable?
The target budget applies your own unit-price target; it is not an appraisal.
The access result is a numerical reference under general rules.
Before contracting, verify the building-line drawing, local ordinances, facility plans, daylight, parking, height, use and construction costs, and document any necessary contract conditions.
Official sources, updates and your next action
The National Law Information OPEN API was searched directly and the relevant article details were checked.
Building Act ID001823/MST273437 was promulgated on 2025-08-26 and took effect on 2026-02-27.
Decree ID002118/MST290833 was promulgated and took effect on 2026-10-06.
Both search records were marked current when verified on 2026-10-20.
Review these width, length, angle and floor-area thresholds annually and whenever the legislation changes.
Immediately before buying a specific parcel, recheck its designated building line, road notice, local ordinances, facility exception and measured geometry.
Enter your current evidence, save the review, and confirm the exclusion drawing and planned scale with the authority/architect before negotiating effective unit cost.