Volume and bags
Use it for slabs, pads, footings and rectangular pours when you know length, width and thickness.
Open concrete calculatorMetric construction estimators
Free construction calculators
Estimate concrete volume, floor slabs, cement bags, paint, tile boxes, roofing sheets, drywall materials, solar panels, BTU load and lighting needs before you quote or buy.
- 17 free tools
- Metric units
- No registration
- Reference estimates only
Start with the most used calculators
These tools cover the first questions most people ask when planning a small construction or renovation job.
Concrete, gravel and mesh
Estimate a slab on grade with gravel sub-base, concrete volume and wire mesh area.
Open slab calculatorPaint and tile
Calculate liters of paint, tile boxes, waste allowance and coverage before buying materials.
Open paint calculatorSolar, BTU and lighting
Plan basic capacity for panels, room conditioning and light fixtures with clear assumptions.
Open solar calculatorPractical estimating guides
Read the method first, then open the related calculator with your own project dimensions.
How to calculate concrete for a slab
Length, width, thickness, waste allowance and a worked metric slab example.
Read guideHow many cement bags for a slab
Estimate bags from slab volume, cement content per cubic meter and bag weight.
Read guideHow much paint for a room
Calculate wall area, openings, coats, coverage and approximate cans.
Read guideBrowse all calculators
Search by material, trade or project type. Filters can help narrow the list when you already know the category.
Showing calculators
No calculator matches that search. Try "concrete", "paint", "tile", "roofing" or "solar".
Solar Panel Calculator
Estimate number of panels, system size in kWp and approximate monthly generation.
Open calculatorBTU Calculator
Estimate heating or cooling load in BTU/h, kW and tons for a room.
Open calculatorLighting Calculator
Estimate light fixtures, lux level and total wattage by room type.
Open calculatorStair Calculator
Calculate steps, riser height, tread depth and stringer length.
Open calculatorConcrete Calculator
Concrete volume, waste allowance, cement bags, sand and gravel.
Open calculatorFloor Slab Calculator
Concrete volume, gravel sub-base and wire mesh for a ground slab.
Open calculatorCement Bags Calculator
Cement bags for concrete, mortar, stucco and lean mixes.
Open calculatorMortar Calculator
Cement and sand quantities for mortar beds, render coats and masonry.
Open calculatorBrick Wall Calculator
Bricks or blocks, cement bags and sand for a masonry wall.
Open calculatorRoofing Calculator
Inclined roof area and estimated number of metal roofing panels.
Open calculatorDrywall Calculator
Drywall panels, studs, tracks, screws and joint tape for partitions.
Open calculatorMetal Stud Calculator
Metal studs, tracks, cladding panels and screws for light partition walls.
Open calculatorDrop Ceiling Calculator
Ceiling panels, support grid length and screws for suspended ceilings.
Open calculatorPaint Calculator
Wall area, coats, coverage, liters and gallons for room painting.
Open calculatorTile Calculator
Tile boxes, area with waste and adhesive estimate for floors or walls.
Open calculatorLaminate Flooring Calculator
Boxes of laminate, hardwood or vinyl plank flooring with waste included.
Open calculatorStucco Calculator
Bags of stucco, render or plaster by area, thickness and number of coats.
Open calculatorHow to use the estimates
CalculaObra helps you prepare a first material list before requesting quotes, comparing supplier options or checking a contractor proposal.
Measure the actual work area
Use real site measurements whenever possible. Small errors in length, width or thickness can create large differences in quantities.
Add a realistic waste allowance
Waste depends on cuts, breakage, irregular geometry, transport, product format and installation quality.
Confirm with suppliers or a pro
Use the result as a planning baseline, then confirm product coverage, packaging, local availability and technical requirements.
What CalculaObra does and does not do
The calculators are designed for preliminary planning. They make assumptions visible, but they do not replace professional judgement.
What it does
- Estimates material quantities from simple dimensions.
- Helps compare quotes and supplier quantities.
- Shows formulas, assumptions and common mistakes.
- Supports metric planning for small construction work.
What it does not do
- It does not design structural elements.
- It does not guarantee final material quantities or prices.
- It does not replace local building code review.
- It does not certify contractors, suppliers or products.
Technical disclaimer
All results from CalculaObra are reference estimates only. They do not replace the formal calculation, design, engineering review or budget of a qualified professional. Quantities and costs vary by location, materials, labor, transport and actual site conditions.
Frequently asked questions
Short answers before you use the calculators for a real project.
Are the construction calculators free?
Yes. The calculators are free to use and do not require registration.
What units do the calculators use?
They use metric units such as meters, square meters, cubic meters, kilograms and liters. Some pages also mention common imperial equivalents.
Can I use the results to buy materials?
Use the results as a planning baseline only. Always verify site measurements, product coverage, waste allowance and supplier requirements before buying.
Do these calculators include local prices?
Most English calculators focus on quantities and material estimates. Optional price fields are reference inputs entered by the user, not guaranteed market prices.
Do the calculators replace a professional estimate?
No. They support preliminary planning and do not replace structural design, engineering review, code compliance or a formal contractor quote.