Paint Coverage, Coats and Can Combination Calculator

Estimate undiluted paint and water from measured areas, coverage and coats.
Compare lowest-cost and least-leftover can combinations using your prices.

Calculate one product, color and finish at a time. Water never reduces the paint purchase quantity.

Use coverage per coat of undiluted paint and actual supplier can prices. Allowance and dilution inputs are not manufacturer recommendations.

1. Walls and ceiling to paint

Area input mode

Room length (m)Room width (m)Wall height (m)Wall opening deductions (m²)

Paint the ceiling with the same product

Room mode uses walls 2×(length+width)×height and ceiling length×width. For irregular spaces or several rooms, enter summed areas for the same paint. Deduct only openings you will not paint.

2. Product coverage and coats

Lower coverage per coat (m²/L)Upper coverage per coat (m²/L)Number of coats (1–10)Extra allowance (%)Water / undiluted paint (%)

If you have one coverage value, enter it in both fields. A 10% allowance means theoretical quantity×1.10. Dilution is water volume relative to undiluted paint; leave 0% when not permitted or not needed. Do not enter two-coat coverage as a one-coat value.

Product, TDS version/date, substrate and supplier notes (optional)

3. Can sizes and prices for the same product

Price currency (no conversion)

Can option 1

Name (optional)Undiluted volume (L)Price per can (KRW)

Sizes: 0.01–100 L. Use up to two decimals for sizes and prices, with consistent tax inclusion. Assumes unlimited stock and per-can prices; shipping and bundle discounts are excluded.

I have checked undiluted coverage per coat, matching product/color/finish and the manufacturer’s permitted water dilution.

Results

Complete the inputs and calculate. Recalculate after changing any input.

Software limits: dimensions 0.01–100 m; each direct area/deduction 0–10,000 m²; coverage 0.1–100 m²/L; percentages 0–100%; price 0–10 million; required paint 2,000 L. These are not manufacturer-approved limits.

Separate paint demand from the cans you buy

This paint coverage, coats and can combination calculator subtracts unpainted openings from walls and ceilings, then uses product-specific coverage to estimate undiluted paint demand.
It helps households planning a room refresh, a rental turnover or other measured repair work prepare a purchase list.
Floor area alone does not capture wall height, openings or whether the ceiling is included.

Paint demand is continuous, but cans are purchased in whole numbers.
A large can with a low price per liter can still cost more overall if it leaves too much surplus.
The tool compares a lowest-cost combination with a least-leftover combination among your entered options.
Product selection, color choice, labor and a complete renovation quote remain separate decisions.

Measure walls, ceilings and openings

Rectangular room mode

Enter room length, width and wall height in meters.
Gross wall area is 2×(length+width)×height; ceiling area is length×width.
The ceiling is added only when selected.
Deduct doors, windows and other surfaces you will not paint with this product, including any deliberately unpainted areas behind fixtures.

Direct area mode

Use measured gross surface areas for corridors, irregular walls or several rooms.
Sum each wall before subtracting openings once.
If you already entered net area, set the deduction to zero to avoid subtracting it twice.
Ceiling deductions are separate from wall deductions.

Deductions exceeding their corresponding wall or ceiling area block the calculation.
Unused ceiling fields are ignored when the ceiling is excluded.
When the ceiling uses a different product, color or finish, exclude it and create a separate purchase list.

Read product coverage and coat instructions

Coverage means square meters painted once per liter of undiluted paint, in m²/L.
Use the manufacturer’s technical data for the exact product, finish and application method.
A package label describing the finished area after two coats is not a one-coat coverage value.
Confirm the coat basis and undiluted-paint basis before entering an ambiguous specification.

Compare both coverage endpoints

Enter the lower and upper coverage values from the product information.
Higher coverage means less paint; lower coverage means more paint.
If only one verified value is available, enter it in both fields.
These endpoints are scenarios, not a probability interval or a guarantee: substrate absorption and film conditions still need confirmation.

Coats count repeated applications of the same paint.
Calculate primer and topcoat separately when they are different products.
The tool does not decide how many coats will hide an existing color.
Record the product, color, sheen, TDS version and date in the notes so your supplier can review the same assumptions.

Extra allowance and dilution are different inputs

Allowance increases paint demand

Extra allowance adds a percentage to theoretical paint demand.
A 10% allowance multiplies theoretical demand by 1.10.
It is not a loss fraction applied to the purchased volume, which would require a different formula.
Choose a supported project assumption for material left in tools or other practical needs; the tool does not prescribe a standard allowance.

Water does not replace paint

Water dilution is a volume ratio relative to undiluted paint.
A fictional 10% ratio multiplies planned paint demand by 0.10 to show water separately.
It never reduces the amount of paint to buy.
Leave the field at zero when water is not permitted or needed; do not use it for solvent thinning or weight-based mixing ratios.

Water is calculated for planned paint use including allowance, not for every can purchased.
It is not an instruction to mix all cans at once or dilute paint reserved for later.
Mixture volume is the arithmetic sum of paint and water for planning; follow the product instructions for actual mixing and application.

Formulas and whole-can optimization

A = gross walls − wall deductions + included ceiling − ceiling deductions

Q = A × coats ÷ coverage per coat × (1 + allowance/100)

Water = Q × dilution/100 · Mixture = Q + water

Purchased volume = Σ(can volume × integer count) ≥ Q

Enter can sizes in 0.01 L increments and prices with up to two decimal places.
The search finds sufficient whole-can combinations without rounding the displayed paint demand downward.
For lowest cost, ties favor less purchased volume, then fewer cans.
For least leftover, volume comes first, followed by price and number of cans.

All options must be the same product, color and finish, with enough stock available.
A blank price is missing information, not a free can; remove unused options or complete their prices.
Shipping, bundle discounts, seller-specific minimum orders and return policies are excluded.
Use a consistent tax-inclusive or tax-exclusive basis for all prices, then review excluded costs separately.

Five steps to a purchase list

Define the areas using the same paint and enter measured walls, ceiling and openings.
Keep other products in separate calculations.
Confirm coverage per coat of undiluted paint and the planned coat count.
Repeat a single coverage value in both endpoint fields.
Enter your extra allowance and permitted water ratio, recording the supporting product notes.
Do not treat fictional example values as measured specifications.
Add available can sizes and prices on the same tax basis.
Changing KRW to USD changes the label only: it does not convert entered prices.
Calculate and compare both coverage endpoints, lowest cost and least leftover.
Save the TXT purchase list and confirm substrate conditions, stock and batch with the supplier before ordering.

Worked fictional example: two coats in one room

Consider a room 4 m long, 3 m wide and 2.5 m high, with 5 m² of wall openings and no ceiling paint.
Gross walls total 35 m², net area is 30 m² and two-coat area is 60 m².
Fictional coverage of 10–12 m²/L with 10% extra allowance requires 5.5–6.6 L of paint.
Assuming a permitted fictional 10% water ratio, water is 0.55–0.66 L and mixture is 6.05–7.26 L.

Lowest-cost plans with fictional 1 L cans at KRW 12,000 and 4 L cans at KRW 38,000
Demand and combination	Purchased	Leftover	Price (KRW)
5.5 L needed · 4 L×1 + 1 L×2	6 L	0.5 L	62,000
6.6 L needed · 4 L×1 + 1 L×3	7 L	0.4 L	74,000

The prices, KRW 12,000 per 1 L can and KRW 38,000 per 4 L can, are fictional and are not market averages.
The example indicator remains visible after editing; reset before entering a real project.
Purchase cost may remain unchanged as demand increases within a packaging step, then jump when another can becomes necessary.

Interpret cost and leftover together

The cheapest plan can leave more paint

For 5 L demand, suppose a 6 L can costs 10 and a 5 L can costs 12 in the same fictional currency.
The 6 L can minimizes cost while the 5 L can minimizes leftover.
Compare the saving with storage space and future touch-up needs.
The tool does not determine shelf life or whether stored paint will remain usable.

Leftover is purchased volume minus paint demand including allowance.
Do not add the allowance again as though it were missing from the plan.
A list based only on higher coverage can be insufficient when actual coverage is lower.
Review both endpoints; they do not list every possible purchase plan inside the coverage range.

Use the results for rental refreshes and repairs

Several rooms in the same color

Combine gross areas for the same product instead of rounding each room to cans independently.
In direct mode, keep walls and ceiling separate and deduct each opening once.
When substrates require different coverage assumptions, calculate separately and review the lists together.

Compare available packaging

If suppliers stock different can sizes, enter only the sizes available from the supplier being considered.
Compare the total price of sufficient paint, not just the price on a single can.
Existing paint inventory and its condition are not automatically credited.
The tool does not suggest mixing different products to reduce purchases.

Input limits and practical boundaries

The search supports four can options, each 0.01–100 L, and paint demand up to 2,000 L.
These are software limits, not product application standards.
Dimensions are 0.01–100 m; each direct area and deduction is 0–10,000 m²; coverage is 0.1–100 m²/L; coats are integers from 1–10.
The 100% input cap for allowance and water does not mean the product permits that dilution.
Do not finalize a purchase when coverage data or its undiluted basis is unconfirmed.
Surface preparation and application method still require product-specific review.
Primer, tools, masking materials, delivery and labor require separate budgets.
Include them when comparing with a complete renovation quote.

Frequently asked questions

Can I use floor area alone?

Floor area does not give wall height or opening area.
Enter room measurements or measured gross wall and ceiling areas.

Is the ceiling included automatically?

The ceiling is included only when selected.
Calculate separately if it uses a different color or product.

Can I buy less paint if I add water?

No reduction is made because coverage is based on undiluted paint.
Confirm the permitted water ratio with the manufacturer.

What if the label gives one coverage value?

Confirm it is per coat and per liter of undiluted paint, then enter it in both endpoint fields.
Do not confuse it with finished two-coat area.

Why not buy the largest can first?

Whole-can quantities and different prices can make a mix of smaller sizes cheaper.
The search compares sufficient integer combinations of all entered options.

Can I combine primer and topcoat?

Calculate each product separately because coverage and packaging prices differ.
Use the coat count only for repeated applications of the same product.

Does a blank price mean a free can?

A blank price blocks calculation as missing information.
Enter zero explicitly for a free-can assumption and remember that stock limits are not supported.

What does the saved purchase list include?

It includes areas, coverage, coats, allowance, dilution, can sizes and prices, product notes, example status and results.
Ask the supplier to review stock and substrate conditions against that list.

Sources and product checks

Method sources checked: 2026-09-21.
Benjamin Moore describes paint estimates as approximate and dependent on factors including application method; its calculator assumes two coats and excludes the ceiling.
This tool instead lets you choose coats and ceiling inclusion rather than treating those assumptions as universal.

No product coverage or current selling price is fetched automatically.
Recheck the current technical sheet, packaging, undiluted coverage basis and permitted dilution before ordering.
This is a global metric quantity and purchasing model using KRW or USD input prices; it applies no Korean statutory construction rule or tax rate and does not certify painting quality.

Review your purchase list with the product sheet

Enter measured areas and verified coverage, then compare paint demand and can combinations at both endpoints.
Review leftover, manufacturer conditions and actual stock alongside price.
Save the inputs and purchase list so the supplier can check the same project assumptions.

Calculate paint and can combinations