Building Material Calculator

Your values

Length (ft)

Width (ft)

Wall height (ft)

Slab thickness (in)

Doors

Windows

Waste (%)

Result

Floor area

240 sq ft

Net wall area

461 sq ft

Material	Quantity	Notes
Concrete slab	3.26 cu yd	or 147 × 80 lb bags
Bricks (single wall)	3,478	modular bricks
Drywall	25	4 × 8 ft sheets, walls and ceiling
Paint	4.0 gal	2 coats, buy 4 gal
Flooring	264 sq ft	including waste
Wall studs	64	plus 192 ft of plates

How the estimate was made

Rules of thumb behind each quantity

Concrete: one 80 lb bag of premixed concrete yields about 0.6 cu ft.
Bricks: about 6.9 modular bricks per square foot of single-skin wall with 3/8 in joints.
Drywall: 32 sq ft per 4 × 8 ft sheet, covering walls and ceiling.
Paint: 350 sq ft per gallon per coat, two coats on walls and ceiling.
Studs: about one stud per linear foot of wall at 16 in centres, which allows for corners and openings; plates are three runs of the wall length.

How to Use

Step-by-step instructions

1Enter the inside length and width of the room and the wall height in feet.
2Enter the slab thickness in inches, and the number of doors and windows.
3Set a waste allowance (10% is typical) and read the material list.

Material takeoff

Floor and wall areas drive every estimate: concrete from floor area × slab thickness, bricks and drywall from wall area, paint from walls and ceiling, studs from the wall length.

Net wall area = 2(L + W) × H − openings

Variables:

L, WLength and width of the room (ft)

HWall height (ft)

openings21 sq ft per door, 15 sq ft per window

Example

20 × 12 ft room, 8 ft walls

Inputs:

Size:20 × 12 ft

Wall height:8 ft

Slab:4 in

Openings:1 door, 2 windows

Steps:

1.Floor area = 20 × 12 = 240 sq ft; perimeter = 64 ft.
2.Net wall area = 64 × 8 − 21 − 30 = 461 sq ft.
3.Concrete = 240 × 4/12 = 80 cu ft, + 10% = 88 cu ft = 3.26 cu yd.
4.Drywall = (461 + 240) ÷ 32 × 1.1 = 24.1, so 25 sheets.

Result:

3.26 cu yd of concrete, 3,478 bricks, 25 drywall sheets

Building Material Calculator: the short answer

A building material calculator turns a room's size into a shopping list. For a 20 × 12 ft room with 8 ft walls, a 4 in slab, one door, two windows and 10% waste, you need about 3.26 cu yd of concrete (147 bags of 80 lb), 3,478 bricks for a single-skin wall, 25 sheets of 4 × 8 drywall for the walls and ceiling, 4 gallons of paint for two coats, 264 sq ft of flooring and about 64 studs.

Net wall area = perimeter × wall height − about 21 sq ft per door and 15 sq ft per window.

Add 5% to 15% for waste and offcuts; 10% suits most simple rooms.

One 80 lb bag of premixed concrete makes about 0.6 cu ft.

By the SuperCalX team · Reviewed by Dr. Ahmed Mortuza Saleque, founder and editor · Last reviewed November 3, 2026 · How we check our calculators

The rules of thumb behind each material

Material	Rule used	Based on
Concrete	Floor area × slab thickness; 27 cu ft per cu yd; 0.6 cu ft per 80 lb bag	Bag yields printed by concrete makers
Bricks	About 6.9 bricks per sq ft of wall	Modular brick, 7 5/8 × 2 1/4 in, 3/8 in mortar joints
Drywall	32 sq ft per sheet	4 × 8 ft sheets on walls and ceiling
Paint	350 sq ft per gallon per coat	Typical coverage on primed drywall
Studs	About 1 per linear foot of wall	16 in centres plus corners, doors and windows
Plates	3 × wall length	One bottom plate and a doubled top plate

Estimating more than one room

Run the calculator once per room and add the results, or enter the outside footprint of a simple rectangular building for the slab and exterior walls. Interior partition walls need their own wall area: length × height, counted on both faces for drywall and paint.

For a single material in more detail, use the dedicated tools: brick, drywall, framing, lumber, rebar and gravel for the sub-base under a slab.

Turning quantities into a budget

Multiply each quantity by your local price. With ready-mix concrete at $160 per cu yd delivered, 3.26 cu yd costs about $522; at $7 per 80 lb bag, 147 bags cost $1,029, which is why ready-mix usually works out cheaper for larger pours. Prices vary widely by region, so get supplier quotes before ordering.

Worked examples

20 × 12 ft room, 8 ft walls, 1 door, 2 windows

Floor area = 240 sq ft; perimeter = 64 ft.
Net wall area = 64 × 8 − 21 − 2 × 15 = 461 sq ft.
Concrete = 240 × 4 ÷ 12 × 1.1 = 88 cu ft = 3.26 cu yd, or 88 ÷ 0.6 = 147 bags.
Bricks = 461 × 6.86 × 1.1 = 3,478.
Drywall = (461 + 240) ÷ 32 × 1.1 = 24.1, so 25 sheets.
Paint = (461 + 240) × 2 coats ÷ 350 = 4.0 gallons.

3.26 cu yd concrete, 3,478 bricks, 25 drywall sheets, 4 gal paint, 264 sq ft flooring, 64 studs.

Building Material Calculator FAQ

How do I estimate building materials for a house?

Break the house into rooms and simple rectangles, work out floor and wall areas for each, and apply a rule per material: concrete by volume, bricks and drywall by wall area, paint by area and coats, framing by wall length. Add 10% waste, then check the total with a supplier.

How much concrete do I need for a 20 × 20 slab?

At 4 in thick, 20 × 20 × 4 ÷ 12 = 133.3 cu ft, or 4.94 cu yd. With 10% extra, order about 5.4 cu yd.

How many bricks are in a square foot?

About 6.9 standard modular bricks per square foot of wall with 3/8 in mortar joints, so roughly 690 per 100 sq ft before waste.

Does this replace a contractor's takeoff?

No. It gives quantities for budgeting and first orders. A builder's takeoff also counts headers, blocking, trim, fixings and site-specific waste.

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