# Wall Putty Calculator: How Much Putty and POP for a Room

> A wall putty calculation works out the area to be puttied, the walls less doors and windows plus the ceiling if included, multiplies it by the number of coats, and divides by the putty's coverage per coat from its data sheet. POP punning, where used, is estimated from the area, its average thickness and its consumption for each millimetre.

## What it calculates

The calculator gives, for a room or an area you enter:

- the **area to putty**, walls less doors and windows, plus the ceiling if chosen;
- the **wall putty** in kilograms and whole bags, for the number of coats chosen;
- the **POP punning** in kilograms and whole bags, if chosen.

Putty comes before primer and paint. Once the putty is estimated, use the
[paint quantity calculator](/calculators/paint-quantity-calculator) for the primer and finish
coats on the same room.

## Inputs

**Area** chooses whether the area comes from the room size or is entered directly.

**Room length**, **width** and **wall height** are the inside dimensions in feet. Use the
height to the false ceiling where there is one. **Surfaces** chooses walls only, or walls and
ceiling. **Doors** and **windows** are counts; their sizes are in the assumptions panel.

**Area to putty**, when entered directly, is in square feet and should already be net of
doors and windows.

**Putty coats** is the number of coats in the specification.

**POP punning** adds a plaster of Paris levelling coat before the putty.

The **assumptions** panel holds the putty coverage and bag size, the door and window sizes,
the wastage allowance, and the POP thickness, consumption and bag size.

## Method

1. Area to putty = 2 × (length + width) × height − doors × door width × door height −
   windows × window width × window height, plus length × width if the ceiling is included.
2. Area in m² = area in sq ft × 0.092903.
3. Putty = area in m² × coats ÷ coverage for one coat × (1 + wastage).
4. Putty bags = putty ÷ bag size, rounded up.
5. POP = area in m² × thickness in mm × consumption in kg/m² for each mm × (1 + wastage).
6. POP bags = POP ÷ bag size, rounded up.

If the POP data sheet gives coverage as square metres for each kg at a stated thickness,
convert it: consumption for each mm = 1 ÷ (coverage × that thickness).

## Assumptions

| Assumption | Default | Notes |
| --- | --- | --- |
| Putty coats | 2 | Follow the finish specification |
| Putty coverage, each coat | 2 m² for each kg | Illustrative starting value: replace with the figure on your product's data sheet |
| Putty bag size | 40 kg | Check the bag size of the product you are buying |
| Door | 3 × 7 ft | Change for wider or double doors |
| Window | 4 × 4 ft | Change to your window sizes |
| Wastage | 10% | Mixing losses, droppings and sanding |
| POP thickness | 3 mm | Average over the wall; used only with POP punning |
| POP consumption | 1 kg/m² for each mm | Illustrative starting value: replace with the figure on your product's data sheet |
| POP bag size | 25 kg | Check the bag size of the product you are buying |

Coverage is the input that matters most. Data sheets give it for a reasonably level surface;
on rough or uneven plaster, site coverage is usually lower.

## Limitations

- **Rectangular rooms only.** Add walls of other shapes separately, or enter the area.
- **Openings are averaged.** Rooms with full-height glazing or many doors should use their
  real opening sizes, or enter the net area.
- **POP thickness is an average.** Badly out-of-plumb walls vary in thickness from place to
  place; measure before relying on the figure.
- **Products are sold in fixed bag sizes.** Round to the packs available, and buy from one
  batch where the finish matters.
- **It does not choose the system.** Whether a wall needs POP punning, putty, or neither, and
  how many coats, is a decision for the finish specification.

## Worked example

A 20 ft × 15 ft room with 10 ft walls, one door and two windows, walls only, two coats of
putty at 2 m² for each kg a coat, 40 kg bags and 10% wastage:

| Step | Calculation | Result |
| --- | --- | --- |
| Gross wall area | 2 × (20 + 15) × 10 | 700 sq ft |
| Openings | 1 × 3 × 7 + 2 × 4 × 4 | 53 sq ft |
| Area to putty | 700 − 53 | 647 sq ft (60.1 m²) |
| Putty | 60.1 × 2 / 2 × 1.10 | 66.1 kg |
| Putty bags | 66.1 / 40, rounded up | 2 |

The room needs about **66 kg of putty, or 2 bags of 40 kg**. Puttying the ceiling as well
adds 300 sq ft, taking the area to 947 sq ft (88 m²) and the putty to 96.8 kg, or 3 bags.
With POP punning on the walls at 3 mm and 1 kg/m² for each mm, the POP is 198.4 kg, or 8 bags
of 25 kg.

## How engineers use it

On a fit-out, wall finishes are measured from the drawings in square metres for each finish,
and the specification sets the full system: surface preparation, any POP punning, putty
coats, primer and finish coats. Material quantities then follow from the manufacturers'
coverage for that system. A calculation like this one is the quick check that a supplier's
or painter's material estimate is in the right range.

## When a professional design must replace it

Use the calculator to estimate how much putty and POP to buy for a room or to check an
estimate. Replace it with a measured take-off and a written finish specification for a whole
office or building, where surfaces, backgrounds and finishes vary from room to room and where
the preparation work is a large part of the job.

## Frequently asked questions

### How many bags of wall putty do I need for a room?

Work out the area to putty in square metres, multiply by the number of coats, divide by the coverage for one coat from the data sheet, add a wastage allowance, and divide by the bag size, rounding up. A 20 by 15 ft room with 10 ft walls, one door and two windows needs about 66 kg, or 2 bags of 40 kg, for two coats at 2 m² per kg each coat.

### What coverage should I use for putty?

Use the figure on the product's data sheet. Many data sheets state coverage for two coats together; double that figure to get the coverage for one coat, because the calculator multiplies by the number of coats. Coverage falls on rough or uneven plaster, so site figures are usually lower than the data sheet.

### What is the difference between POP punning and wall putty?

POP punning is a levelling coat of plaster of Paris applied over uneven plaster, usually a few millimetres thick, to give a true surface. Wall putty is a thinner skim applied after it, or directly on reasonably level plaster, to fill fine pores and give a smooth base for primer and paint.

### Is primer or paint included?

No. Primer and paint come after putty and are estimated separately from their own coverage. Use the paint quantity calculator on this site for the primer and finish coats, with the same room size.

### Should I include the ceiling?

Only if the ceiling is being puttied in the same exercise. In offices the ceiling is often a false ceiling with its own finish, in which case choose walls only and measure the wall height to the false ceiling.

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Source: https://hagerstone.com/calculators/wall-putty-calculator