Free construction calculators that show their work

Estimate concrete, masonry, rebar and more, with the formula, assumptions and listed sources shown. Measure in feet and inches, no sign-up.

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  • Formula shown
  • Assumptions shown
  • Sources listed
  • No sign-up
Construction estimating illustration: a concrete slab measured with a tape measure, a rebar grid, concrete blocks and cement bags
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ft + in
Measure on site
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Formula and assumptions

Popular construction calculators

Concrete CalculatorYards, Bags, Weight & Cost→Concrete Slab CalculatorYards, Bags & Cost→Rebar CalculatorSlab Grid, Length & Weight→Concrete Block CalculatorBlocks & Mortar→Paver CalculatorPavers & Bedding Sand→Brick CalculatorHow Many Bricks and Mortar→

Every calculator

Concrete & Masonry hub →

Pick a calculator by what you are building: concrete pours, masonry walls, or the materials and reinforcement that go with them.

Concrete pours
Cubic yards, bags and cost for slabs, footings, round columns, stairs and curbs.
Concrete CalculatorYards, Bags, Weight & Cost→Concrete Slab CalculatorYards, Bags & Cost→Concrete Footing CalculatorYards & Bags→Sonotube CalculatorConcrete for Tube Forms→Concrete Stairs CalculatorYards & Bags→Curb and Gutter CalculatorConcrete Yards & Bags→
Masonry walls
Block and brick counts, the courses, and the mortar to lay them.
Concrete Block CalculatorBlocks & Mortar→Cinder Block CalculatorBlocks & Mortar→Block Wall CalculatorBlocks, Courses & Mortar→Brick CalculatorHow Many Bricks and Mortar→Brick Wall CalculatorBricks, Courses and Mortar→Retaining Wall CalculatorBlock Count→
Materials and reinforcement
Mortar, pavers, and the rebar grid that holds a slab together.
Mortar CalculatorBags for Block & Brick→Paver CalculatorPavers & Bedding Sand→Rebar CalculatorSlab Grid, Length & Weight→
More calculators
More construction calculators on the site.
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Latest concrete guides

Fresh, practical guides that explain the math and the money, each linked to the calculator that does it for you.

A mason laying red brick with mortar on a garden wall, measuring the brick wall cost per square foot jobBrick Wall Cost Per Square Foot WorksheetEstimate a brick wall by identifying the wall system first, then measuring face area and applying quotes…Read the guide →A builder measuring a concrete mix ratio by shovelling cement, sand and gravel into a mixer on siteConcrete Mix Ratio: Cement, Sand and AggregateA concrete mix ratio states the relative parts of cement, sand and coarse aggregate.Read the guide →A concrete finisher screeding a fresh slab pour beside a tape measure marking square footage on a job siteConcrete Slab Cost Per Square Foot WorksheetA slab budget starts with approved length, width and thickness, then adds base preparation, reinforcement…Read the guide →A mason laying a brick wall course by course with a trowel and mortar on a residential job siteBrick Wall Cost WorksheetBuild a brick-wall worksheet from the chosen wall system, face area, brick count and product yield, then…Read the guide →A finishing crew pouring and screeding a fresh concrete slab from a ready-mix truck on a residential jobsiteConcrete Slab Pour Cost WorksheetEstimate a slab pour from approved area and thickness, then separate concrete supply, base, reinforcement…Read the guide →A round cardboard tube form set in a dug hole for a deck footing being filled with wet concreteHow to Size Deck FootingsDeck footing dimensions depend on the applicable code table or engineered design, including tributary are…Read the guide →

Why builders use these construction calculators

Four reasons these calculators earn a place in your bookmarks.

Every formula shown

No black boxes. Each calculator prints the exact formula and a worked example.

You check the math instead of trusting it, which matters when you are ordering a truck of concrete.

Assumptions and sources shown

Each page displays its formula, assumptions and a list of sources for readers to inspect.

Check that the listed source and product assumptions match the material you plan to use.

Formula checks during the build

Formula and declared-case checks run during the build; sources are listed for readers to review.

Use the shown formula, your project measurements and the listed sources when deciding what to order.

Free and embeddable

No sign-up, nothing to install. Use any calculator instantly.

Share a link with your numbers, or drop the calculator into your own site for free.

How to estimate concrete and masonry

Two materials, two methods. Knowing which one you are dealing with is half the job.

Concrete is measured by volume

Length times width times thickness gives cubic feet; divide by 27 for cubic yards.

Check the calculated quantity against the yield printed on the selected product and compare current supplier terms for bags and delivery.

Masonry is counted by the unit

Wall area times the units per square foot gives the count: 1.125 blocks or 6.75 modular bricks per square foot.

Add the courses and the bags of mortar, and the wall is planned. A waste factor covers the cuts at corners and openings.

Concrete and masonry estimating, at a glance

The numbers behind the calculators, the ones worth remembering.

27 ft³
in a cubic yard

Concrete is sold by the cubic yard. Divide your volume in cubic feet by 27 to get yards.

45 bags
per yard (80 lb)

At a stated yield of about 0.60 ft³ per 80 lb bag, one cubic yard corresponds to roughly 45 bags. Check the selected product label before ordering.

1.125
blocks per ft²

A standard 16 by 8 inch block covers 0.889 ft², so a square foot of wall takes 1.125 blocks.

6.75
modular bricks per ft²

A nominal modular brick face, including its mortar joint, covers about 21.33 in²: 144 divided by 21.33 gives 6.75 bricks per square foot.

+10%
waste allowance

The ground is uneven and you cannot top up a pour, so order 5 to 10% over and round up.

12-18 in
rebar spacing

Typical on-center grid for slabs; go tighter for driveways and heavier loads.

4 in
standard slab

Four inches suits patios and walkways; use 5 or 6 inches for driveways and vehicle loads.

8-9 bags
mortar per 100 block

An 80 lb bag of pre-mixed mortar lays about 12 blocks at 3/8 inch joints, so 8 to 9 bags per 100, and about 28 per 1000 bricks.

How every Calcnaut calculator works

The same standard runs through all of them.

Measure in feet and inches

Enter dimensions the way you measure on site.

No converting to decimals in your head, and lengths accept both feet and inches.

Waste built in

Each result includes a waste allowance you can adjust.

Ready-mix is rounded up to the nearest quarter yard, the way it is ordered, so you do not run short.

Share and print

Every result has a link that holds your exact numbers.

Plus a clean print or PDF and a copy button, so you can send it straight to a supplier.

Embed free

Drop any calculator into your own site with a single snippet.

It stays live, and it stays yours to share, at no cost.

Construction calculator FAQ

Quick answers on how accurate the calculators are, measuring in feet or metric, how much waste to add, and ordering the right amount of material.

Are these construction calculators free?
Yes. Every calculator on Calcnaut is free to use with no sign-up and nothing to install. You can also embed any calculator on your own website at no cost, with a small attribution link back to the source.
How accurate are the calculators?
Each calculator shows its formula, assumptions and listed sources. Formula and declared-case checks run during the build, but those automated checks are not certification or human review. Results are estimates for ordering materials and do not replace engineered drawings or local building code.
Do I measure in feet and inches or metric?
The calculators are built for the U.S. market, so you measure in feet and inches, and length fields accept both. Results show cubic yards and bags, with a metric cubic-meter figure included on the concrete calculators for reference.
How much waste should I add?
A 5 to 10% waste allowance is built into each calculator and is adjustable. Concrete cannot be topped up once the truck leaves, and masonry loses units to cuts at corners and openings, so ordering slightly over is normal rather than wasteful.
When should I compare ready-mix with bags?
Use the calculated volume and bag count to compare product yield, delivery constraints and current supplier quotes for your project. The concrete calculators show quantities; the supplier determines price and delivery terms.
Can I use these for an odd or L-shaped area?
Yes. Split the shape into rectangles, run each one through the calculator, and add the results. For round columns and piers use the sonotube calculator, which handles the circular area for you.
Can I save or share my result?
Yes. Each result has a share link that holds your exact inputs, so you can bookmark it or send it to a supplier, plus a copy button and a clean print or PDF option. Your last inputs are also remembered in your own browser for next time.
Who is behind Calcnaut?
Calcnaut is published by Calcnaut. Every calculator shows its formula. Formula and declared-case checks run during the build; sources are listed for readers to review. You can read more on the editorial policy and method page.
What size rebar do I need for a slab?
Most residential slabs use number 3 or number 4 bar. Patios and walkways are fine with number 3, while driveways and slabs that carry load usually use number 4 or number 5 on a tighter grid. The rebar calculator sizes the grid and the total length, but always follow your engineer or local code for structural work.
How thick should a concrete slab be?
Four inches is standard for patios, walkways and shed bases. Step up to five or six inches for driveways and anything carrying vehicles, since too thin a slab will crack under load. The slab calculator lets you set the thickness and shows how it changes the concrete and cost.
How should I use the cost fields?
Enter a current local unit price when a calculator provides a cost field. The result applies that input to the estimated quantity; it is not a published market-price quote.