Calculate wall putty or skim coat compound from area, thickness and your product label. Find the material quantity, whole bags or tubs to buy and optional cost.
How much wall putty or skim coat compound do I need?
Multiply the area to skim by the combined average thickness and the product's stated consumption per square metre at 1 mm. Add a suitable working reserve, then divide by the amount in one bag or tub and round up. If your label gives consumption at another thickness, use that reference thickness in the calculator.
This wall putty calculator estimates full-surface wall filler and skim coat quantities. It can use dry powder in kilograms or ready-mixed filler in kilograms or litres. It does not use one universal consumption rate. Copy the values for your exact product and intended application.
Quick instructions
- Enter wall dimensions or a measured total area. Subtract openings you will not skim and add reveals that will receive the same thickness.
- Choose one coat, equal coats or the combined thickness of different coats. Enter an average thickness over the whole selected area.
- Copy the product's consumption or coverage per whole pack, including its reference thickness. Enter the amount in one bag or tub.
- Adjust the reserve, add any usable unopened full packs and calculate. A price is optional.
The example button fills in a 4 × 3 m room with a 2 mm average skim and a product consumption of 1.2 kg/m² at 1 mm. Those are example inputs, not a universal specification for your wall.
Measure the area you will actually skim
For a rectangular wall, area is width × height. Add all walls, or enter repeated walls with the count field. The calculator supports up to twelve wall rows. Choose metres, centimetres, millimetres, inches or feet. Area can be shown in square metres or square feet.
Subtract only windows, doors and other surfaces that receive no filler. Add window reveals and returns if they receive the same product and thickness. A ceiling can be included by treating its length and width as another rectangle, provided the product is approved for ceilings and the thickness is the same.
For sloping or irregular walls, split the surface into rectangles and triangles, calculate their combined area and use measured-area mode. A triangle has area base × height ÷ 2. Measure different thickness zones separately rather than applying the deepest spot to every wall.
Use average thickness, not the deepest hollow
A wall with one 5 mm depression does not necessarily need a 5 mm layer everywhere. Check the surface at several representative points with a suitable straightedge and estimate the average required layer over each zone. Local holes and deep repairs may need a different filler and should be calculated separately.
The thickness must use the same basis as the manufacturer's consumption figure. Do not substitute a desired dry finish thickness for an application thickness unless the technical sheet defines it that way. Drying and shrinkage are product-specific.
Choose one coat for a single application. Choose equal coats if every coat uses the same product at the same average thickness. For example, two 1 mm coats have a combined thickness of 2 mm. If coats differ, select combined thickness and enter their sum, such as 1.5 + 0.5 = 2 mm. The calculator does not multiply that total again.
The optional minimum and maximum fields are the manufacturer's limits for one full-surface coat. In one-coat and equal-coat modes, a value outside your entered limits stops the calculation. In combined-thickness mode, individual coats are unknown, so you must check each coat yourself. An average within a limit does not confirm that every local deep spot is permitted.
Read the consumption and package units
| Label says | What to enter |
|---|---|
| 1.2 kg/m²/mm | Consumption 1.2 kg per m², reference thickness 1 mm, and the bag mass in kg. |
| 1 L/m² at 1 mm | Consumption 1 L per m², reference thickness 1 mm, and the tub volume in L. |
| A whole pack covers 10 m² at 2 mm | Whole-pack coverage 10 m², reference thickness 2 mm, and the amount in that pack. |
The product-label area unit is separate from the room's area unit. One square foot is 0.09290304 m². Changing an area or thickness unit converts the relevant inputs. Changing the label format clears the rate so that an old consumption value cannot silently become coverage.
Use coverage stated for full-surface filling at a known thickness. A claim about covering drywall joints or a specified two-coat system is not automatically a rate per millimetre. If the thickness basis is missing, obtain the appropriate full-surface consumption from the manufacturer before using this tool.
The estimate scales consumption in proportion to thickness. Use that planning relationship only within the product's approved application range and where the label provides a thickness-based rate. A coverage range is not a guarantee. For a cautious estimate, use the higher consumption or lower area covered per pack, as appropriate to your surface.
Dry powder and ready-mixed filler are different quantities
For a powder product, the result in kilograms is the dry material to buy before adding water. Mixing water is not included in the purchase mass and does not increase the amount of dry powder required. Follow the manufacturer's mixing ratio and working time separately.
For ready-mixed filler, enter the mass or volume of the purchased material. A 10 L tub is not automatically a 10 kg tub. The calculator keeps kilograms and litres separate and does not assume a density. Match the consumption unit to the pack unit. If the product data uses a different unit, obtain the matching data or a manufacturer-confirmed conversion first.
As a product-specific example, Weber's Estonian LR+ instructions state approximately 1.2 kg/m² for a 1 mm layer and a 1 to 3 mm full-surface application range. The product is intended for dry rooms. The example button uses this consumption with a 20 kg bag. Check your current local product sheet and packaging before use.
For comparison, Tikkurila's Presto LF+ product information gives an average of 1 L/m² at 1 mm and notes that the required amount depends on the surface. This is a ready-mixed volume-based example. It is not interchangeable with the powder rate above, and it should not be confused with a different product named Presto LF.
Worked example: 32 m² at 2 mm
Two walls are 4 m wide and two are 3 m wide, all 2.5 m high. Their area is 35 m². Subtract 3 m² of openings to obtain 32 m² to skim.
With a 2 mm average layer and consumption of 1.2 kg/m² at 1 mm, the material before reserve is 32 × 2 × 1.2 = 76.8 kg. A 10% reserve adds 7.68 kg, giving 84.48 kg.
With 20 kg bags, 84.48 ÷ 20 = 4.224 bags. Round up to five bags, containing 100 kg. At an illustrative price of €18 per bag, the new purchase costs €90. If one suitable unopened 20 kg bag is already available, buy four more for €72. Total required stock remains five bags.
The 15.52 kg difference between 100 kg in whole bags and the 84.48 kg estimate is caused by pack rounding. The 10% working reserve is already included in the estimate. Do not add either allowance a second time.
Formulas used by the calculator
Net area = measured area − excluded openings + extra area.
Material before reserve = net area × combined thickness ÷ label reference thickness × label consumption per area unit.
With whole-pack coverage: material before reserve = net area ÷ label pack coverage × combined thickness ÷ label reference thickness × pack contents.
Material with reserve = material before reserve × (1 + reserve percentage ÷ 100). Total packs = round up(material with reserve ÷ pack contents). New packs to buy = the greater of zero or total packs minus usable owned packs.
The formulas require matching area and thickness units. The calculator performs those conversions before calculating. The reserve starts at 10% as an editable planning example, not a manufacturer requirement. Adjust it for your application method and realistic handling losses.
Frequently asked questions
How much wall putty is needed per square metre?
It depends on the product and thickness. A label rate of 1.2 kg/m²/mm means approximately 1.2 kg for 1 m² at 1 mm, or 2.4 kg at 2 mm before reserve, within the approved application range. Other fillers can have different consumption and may be sold by volume.
Does a second coat double the quantity?
Only if it covers the same area with the same product at the same average thickness. Two equal coats double one coat's thickness. A thinner second coat uses less. Different base and finish products need separate calculations.
Can I use a drywall joint compound coverage figure?
Use it only if the manufacturer explicitly provides a full-surface skim-coat rate and its thickness basis. Joint filling uses narrow strips and different amounts. This calculator does not infer joint length, tape, screw holes or joint treatment from room area.
How are leftover materials counted?
Enter usable unopened full bags or tubs of the same product and size. Check shelf life and storage condition. Part-used containers are not counted as full packs. The calculator subtracts suitable owned packs from the purchase, while keeping the total job requirement visible.
Are primer, sanding losses and paint included?
Primer and paint need their own product-specific estimates. The editable reserve can allow for reasonable handling and finishing losses, but it cannot compensate for a wrong thickness or an unsuitable surface. Use the paint and primer calculator for the next stage.
Can I paint, wallpaper or apply self-adhesive decor immediately?
Follow the filler, primer and finish instructions for drying, sanding, cleaning and curing. A quantity estimate cannot confirm that a surface is ready. For Decords wall decor, also check the instructions for the exact item and the suitability of the finished wall. If you are planning traditional wallpaper, use the wallpaper roll calculator and wallpaper paste calculator separately.
