Compare window specifications and billing before totals
This per-opening window quotation calculator compares actual written replacement-window offers against one required window schedule.
A low headline total may use a different minimum billed area, omit small windows, substitute a different complete product, or leave out removal and finishing.
Homeowners and family members can identify these differences before signing and ask vendors for a comparable written revision.
Set the common openings first, check the offered complete-window specifications and included quantities, then apply each vendor’s confirmed billing policy.
The tool adds stated installation work and preserves unresolved items instead of treating missing prices as free work.
The currency is KRW, dimensions are millimetres, and area is square metres; Korean general VAT is a 2026 reference rather than a determination of your transaction’s tax status.
All example prices and policies are fictional.
Replace them with measured dimensions and actual written offers.
The tool supplies no market prices, standard minimum area or brand recommendation.
Build one common window schedule
Use a location such as living-room exterior window so that the same opening can be found in the survey and every quotation.
Enter width and height in mm and the number of windows sharing that exact size and specification.
Confirm whether the dimensions refer to the frame exterior or building opening; a glass pane measurement is not automatically the complete-window measurement.
- Each dimension must exceed zero and be at most 20,000mm; required quantity is an integer from 1 to 100.
- Use 1–20 opening rows and compare two or three vendors.
- Separate rows when dimensions, model, glazing, frame or opening method differ.
- Required quantities and vendor-included quantities are separate; a shortage is not automatically filled at an assumed price.
These limits define the input tool, not a safe structural size or manufacturing capability.
When measurements change, obtain confirmation of fabrication, installation and price again.
An excess included quantity is shown without automatically discounting a vendor’s written price.
Check the complete product, even within one brand
The required specification should identify the maker and model, frame configuration, glass thickness and type, colour, interior/exterior arrangement and opening method relevant to the contract.
Copy the vendor’s offered specification separately and select confirmed match, different or unknown.
A shared brand name or similar model label is insufficient by itself to establish equivalent products.
Confirmed match
You have checked that the written complete-window configuration matches the requirement.
This is your confirmation, not a product-performance or workmanship certification by the calculator.
Different or unknown
Amounts can remain useful references, but a like-for-like ranking is withheld.
Entering an extra-cost range does not make a different product equivalent: obtain the revised specification and changed price together.
Recheck confirmations after editing required dimensions, quantities or specifications, or changing an offered product and its billing conditions.
A previous confirmation should not carry over to a new model or pricing basis.
The tool does not derive a whole-window U-value from glass-only performance.
Measured area and billed area are different quantities
Area and billing normalization
Measured area = width mm × height mm ÷ 1,000,000
Required total area = sum of measured area per window × required quantity
Raw area billing units = measured m² per window ÷ m² per billing unit
Raw per-piece units = 1 per physical window
For m² billing, one billing unit is fixed at 1m².
For a custom area unit, enter only the conversion explicitly confirmed by the vendor.
The calculator does not attach a universal conversion to a trade label or turn a glass-selling unit into a complete frame-and-window price.
Minimum quantities and rounding apply per physical window before multiplying by included quantity.
This differs from adding several small windows together and applying one minimum to the total.
If the offer uses a whole-site minimum, mixed product units or additional dimension adjustments, request an itemized revision compatible with this per-opening method.
Interpret minimum units and rounding increments
The minimum is the vendor’s lower billed quantity for each window.
An increment is the step used to round that quantity; a 0.1m² ceiling is appropriate only when the written vendor policy actually specifies it.
Choose exact fractional units, ceiling to the increment, or rounding to the nearest increment to match the offer.
Billed units per window = max(minimum, policy-round(max(minimum, raw units)))
Row billed units = billed units per window × included quantity
Unit-priced row amount = row billed units × written rate per billing unit
Exact mode ignores the increment.
Ceiling and nearest modes first apply the minimum, round to the stated increment, then retain the minimum as a lower bound.
An exact 1.2m² boundary stays 1.2m² under a 0.1m² ceiling rather than becoming 1.3m².
If nearest rounding produces a billed area below measured area, confirm that this really is the vendor’s stated method.
A billed area above measured area does not itself establish improper charging.
The difference describes the effect of the entered minimum, increment, conversion and quantity.
Use unusually large differences to focus the questions you send to the vendor.
Count package prices once
A unit-priced window row multiplies calculated billed units by the written rate.
When several opening rows share one quoted price, create a package and connect those rows to it.
The vendor total counts that package amount once, rather than charging the full package again for each member.
Leave the separate unit price empty on a package-linked row.
Correct packages that have no members and rows pointing to deleted packages.
A package amount does not establish that every required window or specification is included; check its members and quantities separately.
A zero rate means the vendor confirmed no charge.
It is different from a blank or unknown price.
Do not enter zero merely to complete a calculation; invalid required inputs hide the result until corrected.
Align installation, removal, disposal, finishing and lifting
A statement that installation is included does not automatically establish that removal, waste handling and surrounding restoration are included too.
For each of the five work items, select included, separate, unknown or not applicable.
For separately charged work, enter the vendor’s stated lower and upper amounts without adding a charge already included in a window package.
- Installation: confirm the actual fitting and fixing scope after product delivery.
- Removal and disposal: distinguish taking out the old window from transporting and processing the waste.
- Finishing: document required restoration around the frame, sealant and insulation scope.
- Lifting: confirm floor level, access, equipment and the conditions triggering an additional charge.
Other conditional extras must not duplicate these items.
Use a numeric range for furniture moving or uncertain site work only when the vendor has supplied that range.
If the upper amount remains open, preserve it as unknown rather than inventing a contingency percentage.
Distinguish included, excluded and unknown VAT
To align general taxable quotations on a cash basis, VAT-inclusive amounts stay unchanged and VAT-exclusive totals are multiplied by 1.1.
Window rates, packages, separate work and conditional extras must all use the same VAT basis within a vendor.
For mixed bases, obtain a consistent revised quotation before comparison.
Article 30 of Korea’s Value-Added Tax Act provides the general 10% rate verified through the National Law Information OPEN API on November 13, 2026.
The current text, MST276117, is effective January 2, 2026 (2026-01-02).
This does not determine exemptions, zero-rating, special treatment, tax-invoice eligibility, input-tax credits or refunds for a particular transaction.
Select unknown when the tax treatment or quoted basis is unclear.
The tool then withholds the final cash total and overall ranking.
Amounts are summed before the final won rounding; if the vendor rounds individual rows first, confirm the contractual settlement method as well.
Step-by-step use
- Prepare the survey and written offers, then list required locations, dimensions, quantities and complete specifications.
- Copy each vendor’s included quantities and offered specifications, and record whether they match.
- Enter billing units, area conversion, minimum quantity, increment and rounding policy, with written-confirmation status.
- Separate unit-price rows from package members and align the five work scopes plus other extras.
- Confirm a consistent VAT basis, calculate, inspect per-opening differences and copy the vendor question checklist.
- Update the comparison after written replies and use a confirmed installation total for subsequent budget analysis.
Restore the fictional example to learn the result format, but replace its prices and confirmations when entering real quotations.
The unknown-start option helps prepare a review without pretending that outstanding conditions have already been confirmed.
Worked example: a small window’s minimum billed area
The requirement is two 1,200×1,000mm windows and one 600×600mm window.
Measured total area is 1.2m²×2 + 0.36m² = 2.76m².
These are fictional arithmetic examples, not replacement-window market prices.
Vendor A: area pricing
The minimum is 1m², with a 0.1m² ceiling and a KRW 300,000/m² rate.
Billed area is 1.2m²×2 + 1m² = 3.4m², giving KRW 1,020,000 for windows.
Add KRW 100,000 removal and KRW 0–200,000 other conditional extras, then apply excluded VAT: the range is KRW 1,232,000–1,452,000.
Vendor B: package pricing
Both opening rows share one KRW 1,200,000 package including every work item and VAT.
Counting that package once gives a KRW 1,200,000 installed total.
After all product, policy and scope checks are complete, B’s upper total is below A’s lower total.
If A’s upper extra amount, specification or VAT is unknown, some arithmetic can still be shown but the complete comparison is withheld.
Overlapping ranges and equal amounts do not establish an option that is cheaper across all entered conditions.
Workmanship, warranty response and timing need separate review.
Interpret results and request the next written revision
First compare required and included counts, then measured and billed-equivalent areas on area-priced rows.
Per-piece quotations do not bill by area, so no billed-area difference is calculated for those rows.
A shortage or mismatched specification is a question to resolve before comparing money totals.
A conditional total assumes the lower and upper amounts you entered are valid.
An uncapped extra is not treated as zero, and a known subtotal is not a complete installed price.
Only when every vendor is comparable and one vendor’s upper total is strictly below every other lower total does the tool identify the lower option across the entered range.
Use a confirmed project cost only when the required scope, VAT and every charge are confirmed and the lower and upper totals are equal.
Copy it into the linked window energy-payback calculator as the project cost.
If conditional extras remain, obtain a fixed amount first or examine separate explicitly stated scenarios.
This review helps with a living-room-only replacement, a family member’s home or offers mixing large and small windows.
A changed measurement or unavailable product after ordering requires a revised scope and price; do not reuse the old result as a final quotation.
Frequently asked questions
Is billed area above measured area an error?
It may reflect a stated minimum or rounding policy.
The calculator shows the difference without deciding fair pricing or improper charging.
Ask the vendor to explain the unit and minimum in writing.
Can small windows share one minimum area?
This model applies the minimum and rounding per physical window, then multiplies by quantity.
For a whole-site policy, request compatible per-opening details or a separate written calculation instead of applying this formula.
Do package quotations still need opening rows?
Yes.
The package is charged once, but each included window, quantity and specification still needs checking.
Leave member-row unit prices empty to avoid duplicate charges.
Does the same brand establish a specification match?
Check the model, frame, glazing and opening configuration against the requirement.
A shared brand or glass thickness alone does not establish equivalent complete-window performance and contractual scope.
Can I use zero for an unknown extra?
Zero confirms no charge.
Leave unresolved amounts or uncapped upper costs unknown and obtain a written revision.
Outstanding conditions withhold the final total or overall comparison.
Does excluded VAT always mean 10%?
The 10% conversion applies to the general taxable quotation option.
The tool does not decide tax treatment or special cases; confirm exempt, mixed or unclear offers and align their basis first.
Is the lower option a contractor recommendation?
It is a cost comparison across the stated ranges.
It does not assess workmanship, airtightness, condensation, structural safety, delivery, warranties, defect handling or vendor reliability.
Does this calculate energy payback?
This page compares specifications, billing and installation scope.
After the project price is confirmed, enter it and verified whole-window U-values and other required inputs into the separate linked energy-payback tool.
Verified sources and limits
Sources were checked on November 13, 2026 (2026-11-13).
Apart from general VAT, minimum billing, conversions, rounding, prices and included work are vendor-provided inputs.
No universal window minimum area or product price was extracted from these sources.
- Value-Added Tax Act Article 30, official OPEN API
Act ID001571, MST276117, Act No.21065, promulgated October 1, 2025 and effective January 2, 2026; the current text confirms the general 10% rate.
- Published standard interior-construction and window contract PDF
The reference is Fair Trade Commission Standard Terms No.10079, established March 21, 2018 (2018-03-21).
Article 3 paragraphs 3, 5 and 6 address VAT-inclusive contract amounts and itemized scope, quantities, products, specifications and window details; Article 8 addresses agreed work changes.
This is not a claim that the 2018 document is the latest 2026 revision or a determination of contractual legal effect.
- Government announcement introducing the standard contract
The April 25, 2018 announcement explains its introduction and the purpose of separate work details.
Recheck the applicable version, revised quotation and tax treatment for the actual contract.
Request comparable written quotations
Copy the checklist of missing quantities, specification differences, unresolved billing policies and omitted work for each vendor.
Update the scope and prices after written replies so that headline totals can be explained on the same basis.
Once the installed total is confirmed, continue with the overall renovation budget or energy-payback review.