Estimating Construction Materials: A Guide for Contractors (With Formulas)

Estimating construction materials requires skills similar to those of a mathematician, detective, and strategist. 

Every calculation you make can impact the success of your construction project. Get it right, and you’ll be on track. Get it wrong, and you might run into financial problems or major delays. 

In this article, we’ll explore three ways to estimate the cost of construction materials. We’ll break down how the price per unit, square foot, and rule-of-two methods work. Plus, we’ll review the formulas for estimating common building materials and include tips to help you calculate costs. 

5 Tips on Calculating Material Costs

Estimating construction materials involves calculating the quantity and cost needed for a building project. Accurate estimates help you set a budget and price the project fairly. It’s also important to make sure you have the right amount of materials to complete the work. Buying extra materials you won’t use wastes valuable time and money.

Calculating building materials accurately saves time and money. If you don’t assess and plan properly, you might run out of supplies or buy too much, which can go to waste.

Before we go into how to calculate your materials estimates, here are five tips for better estimate decisions.

1. Choose Materials

Count all items needed for your project before starting to avoid budget issues and delays. Create a detailed list that includes everything from windows to light switches. Missing even small things can ruin your budget and cause delays. Review your building plans room by room, indicating where each item will go. 

FROM ONE OF OUR PARTNERS — Commercial Construction vs. Residential Construction: 6 Differences You Should Know

2. Measure Thoroughly

Always measure twice before calculating material costs to avoid mistakes. Use a reliable tape measure, write down your measurements, and check corners and tight spaces using accurate measuring tools. Sketch your measurements and review them before ordering, as suppliers often don’t accept returns on cut materials. 

Carpet, paint, tile, and concrete projects depend on accurate area calculations. Measure each room’s height and width, and add a 10% waste margin.

3. Determine Project Timelines

Having a clear idea of when you expect to complete each stage lets you plan to order materials effectively. For example, say you’re renovating a kitchen. If you know that you need the sink to install the countertops, make sure they’re ordered on time. The plumbing for the sink might come after.  

4. Use Estimating Software

Estimating software saves time and minimizes math errors in building projects by calculating material costs using current supplier prices. The software accurately calculates areas, volumes, and waste percentages and instantly tracks project changes, allowing for cost adjustments when modifications occur.

5. Add an Error Margin

Add a 10–15% margin to your material estimates for waste and mistakes. An error margin helps protect your budget and keeps your project on track, just in case. Plus, customers won’t be surprised by unexplained costs if you need to reorder more of a material mid-project. 

Calculating Materials With the Unit Pricing Method

Unit pricing is a method for calculating costs by dividing work into repeated, measurable units. You set a fixed price for each project unit, such as per square foot or hour. This method saves time and improves estimating accuracy on repetitive tasks like flooring, drywall, or painting.

Here’s an example of using the unit pricing method to calculate the cost of a flooring installation.

1. List All the Material Costs

Collect all material expenses for a completed flooring job. That might include:

• Flooring materials (tiles, hardwood, or laminate)
• Underlay 
• Adhesives
• Grout or transition strips
• Tools 
• Finishing materials, like polish
• Cleaning materials

2. Measure the Square Footage

Accurately measure the total square footage of the flooring you need to install.

3. Calculate the Material Cost per Square Foot

Divide your total material costs by the total square footage to find the rate that helps you break even. 

If you spent $3,600 on materials for a 1,200-square-foot job, your rate is $3 per square foot.

4. Apply to New Projects

After calculating the unit price, you can use it as a standard to estimate building costs for future projects. Multiply the square footage by your established rate for a new project.

5. Calculate Labor Costs per Square Foot

Covering material costs doesn’t pay for your time. Here’s how to factor your labor into the cost:

• Total your labor costs from a previous flooring job. If it took you six hours and you charge an hourly rate of $30, you had $180 in labor costs for that job.
• Divide by the total square footage. For the same job, your labor cost would be $0.15 per square foot.
• Use this rate to estimate labor for projects. A rate of $3.15 would cover labor and material costs. If you charge $3.50 per square foot, you’d be earning $0.35 profit for each unit.

The unit pricing method creates a reliable, repeatable system for future projects.

Calculating Materials With the Square Foot Method

The square foot method estimates project costs by multiplying the total floor area by the price per square foot. For instance, if construction costs $200 per square foot, a 2,000-square-foot house would be estimated at $400,000.

This method also calculates material needs based on usage per square foot, drawing from past projects or guidelines. A house typically requires about 1.1 square feet of flooring material per square foot, so for a 200-square-foot room, you’ll need 220 square feet of flooring.

The square foot method offers quick cost estimates, making it useful for early planning and facilitating initial customer discussions.

Calculating Materials With the Rule of Two Method

The rule of two in construction suggests doubling your material estimate to cover labor, overhead, and unexpected expenses.

For a flooring project in a 200-square-foot room, if laminate flooring costs $3 per square foot, the material cost is $600. When applying the rule of two, it doubles to $1,200. This total accounts for labor, underlayment, baseboards, delivery, and unforeseen costs. 

Using the rule of two gives you a conservative estimate and helps avoid cost overruns by including a buffer for unexpected expenses.

RELATED ARTICLE — How to Price Flooring Jobs 

How to Estimate Common Building Materials

Estimating construction materials, or quantity takeoff, means making a detailed list of everything a project needs based on blueprints. 

This list is organized by construction stages, from the foundation to the roof, and includes items like nails and trusses but not labor or equipment costs. A rough estimate helps determine whether the project is possible. You’ll need a detailed estimate to choose materials and get prices before starting construction.

You need to know the following before you start the estimate:

1. What is the total square footage of the area?
2. How do suppliers sell the construction materials (sheets, bags, bundles, or by weight)?
3. How much does one unit cover?
4. What does one unit cost (price per sheet, bag, or bundle)?

5 Common Building Materials and How to Estimate Costs

Here are some common construction materials and how you can estimate the costs.

1. Concrete

Concrete trucks deliver by the cubic yard. To figure out how many cubic yards you need:

• Multiply length × width × thickness (all in feet).
• Then divide by 27.
• That’s your cubic yards.

Note: When you calculate your space in cubic feet (length × width × thickness), you need to divide by 27 to convert it to cubic yards, which is how concrete companies sell and deliver their concrete.

For smaller jobs where you buy bags from the store, follow these steps:

• Use the online calculator on Quickrete’s website.
• Type in your project size.
• It tells you how many bags to buy.

2. Lumber

Regular lumber (2×4s) sells by the piece. Stores sell hardwood and special sizes by the “board foot.” Here’s how to calculate board feet:

• Multiply thickness (inches) × width (inches) × length (feet).
• Then divide by 12.

Note: The division by 12 in the board feet formula is because one board foot equals 144 cubic inches (12″ × 12″ × 1″), the standard unit of measurement for lumber.

A piece of wood measures one board foot when we define it as:

• 1 foot long (12 inches)
• 1 foot wide (12 inches)
• 1 inch thick
• 12″ × 12″ × 1″ = 144 cubic inches

3. Framing

Here’s how to calculate how many wall boards (studs) you need:

• Measure all your walls and add up the total length in feet.
• Studs are usually spaced 16 inches apart. Multiply your total length by 0.75 to find how many regular studs you’ll need.
• Add more for each corner, places where walls meet, and doors or windows.

4. Drywall

Here’s how to estimate how many sheets of drywall or wall boards you need:

• First, find your total wall space. Measure the height and width of each wall by feet, then multiply the height by the width. Add the footage of each wall for the total space.
• Figure out how many sheets you need. If using 4′ × 8′ sheets (32 square feet each), you’d take your total square footage and divide by 32. 

RELATED ARTICLE — How to Price a Drywall Job

5. Roofing

For roofing materials, you follow similar steps to calculating drywall:

• Calculate how many “squares” your roof is by measuring your total roof area in square feet. Divide that number by 100 to get the squares. For example, 1,700 square feet ÷ 100 = 17 squares.
• Calculate how many shingles you need. Each square requires three bundles of shingles. If you have 17 squares, that means you need 51 bundles of shingles. 
• Calculate how much tar paper you need to lay under shingles. Each roll usually covers four squares, so divide the number of squares you need by 4. For 17 squares, you need 4.25 rolls. 

You also need to complete a drip edge, which is the metal strip around the edges. Measure both the bottom and slanted edges, then add those numbers together. 

Note: Always check the product labels. Some brands have different dimensions which impacts calculations. If you’re struggling with calculations, Joist has a roofing cost calculator you can use to simplify the process. 

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Get started today and see how easy it is to simplify your estimating process.