Free construction calculators that show their work

Estimate concrete, masonry, rebar and more, with the exact formula shown, real material data, and a waste factor built in. Measure in feet and inches, no sign-up.

No calculator matches that yet. Try another term.

  • Exact formula shown
  • Real material data
  • Waste factor built in
  • No sign-up
Construction estimating illustration: a concrete slab measured with a tape measure, a rebar grid, concrete blocks and cement bags
24
Free calculators
$0
No sign-up, ever
ft + in
Measure on site
ASTM
Standards-based

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→

All concrete and masonry calculators

Concrete & Masonry hub →

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

Latest concrete guides

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

A homeowner pouring bagged concrete mix into a round post hole beside a wooden 4x4 fence postHow Many Bags of Concrete per Fence Post?A standard 4x4 fence post set in a 10-inch hole needs about 2 to 3 bags of 80-lb concrete mix, or 3 to 4…Read the guide →A cardboard sonotube form standing in a dug hole being filled with wet concrete for a deck footingHow Much Concrete for a Deck Footing?A standard 12-inch sonotube footing poured 4 feet deep takes about 3.1 cubic feet of concrete, close to 3…Read the guide →A mason buttering mortar onto a concrete block while building a gray block wall on a job siteHow Many Bags of Mortar Per 100 Block?You need about 3 bags of masonry cement mixed with sand, or roughly 8 to 10 bags of pre-mixed 80 lb morta…Read the guide →A mason spreading mortar with a trowel while laying a red brick wall on a job siteHow Much Mortar for 1000 Bricks?You need about 7 bags of masonry cement mixed with sand, or roughly 27 to 28 bags of pre-mixed 80 lb mort…Read the guide →A finished 12x12 concrete slab with a broom finish curing in a residential backyard on a sunny dayHow Much Does a 12x12 Concrete Slab Cost?A 12x12 concrete slab costs about 1,000 to 2,600 dollars installed in 2026, or roughly 6 to 12 dollars pe…Read the guide →A 10x10 foot concrete slab form staked out and ready for pouring in a residential backyardHow Much Concrete for a 10x10 Slab?A 10x10 concrete slab at the standard 4 inch thickness needs about 1.36 cubic yards of concrete, which wo…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.

Real material data

Bag yields, unit sizes, rebar weights and coverage come from manufacturer spec sheets and standards.

We use figures like ASTM A615 and ACI 332, not round numbers invented for a web page.

Tested, not guessed

Every formula runs through automated tests against manufacturer specs and ASTM and ACI standards.

So the numbers match how jobs are actually estimated, not just how they look on paper.

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.

An 80 lb bag yields about 0.60 cubic feet, so bags suit small pours and ready-mix wins above roughly one cubic yard.

Masonry is counted by the unit

Wall area times the units per square foot gives the count: 1.125 blocks or 6.86 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)

An 80 lb bag yields about 0.60 ft³, so a yard takes roughly 45 bags. That is why big pours go ready-mix.

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.

6.86
bricks per ft²

A modular brick with its mortar joint covers about 21 in², or 6.86 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 uses the standard formula and real material data from manufacturer spec sheets and standards like ASTM and ACI, and the math is verified by a test for every release. Results are reliable estimates for ordering materials, but they do not replace engineered drawings or local building code, which take precedence for structural work.
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 use ready-mix instead of bags?
For a small pour, bags are easiest and cheapest. Once a job passes about one cubic yard, which is roughly 45 bags of 80 lb mix, ready-mix delivered is cheaper and far less work than mixing by hand. Each concrete calculator tells you which way to go.
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 built around correct, transparent estimating. Every calculator shows its formula in full and is cross-checked against manufacturer spec sheets and industry standards like ASTM and ACI, with the math verified by an automated test on every release. You can read more on the about 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.
Can I trust the cost estimates?
The cost figures are realistic 2026 ranges for the U.S. market, useful for planning a budget, but prices vary a lot by region, supplier and load size. Treat them as a starting point and get local quotes before you commit, especially on larger jobs.