m, m², m³, kg and liters
Most formulas are based on simple metric geometry: area, volume, coverage rate, waste factor and package size.
Free online construction estimators
Free construction calculators
Estimate concrete volume, drywall sheets, metal studs, tile boxes, paint gallons, roofing panels, solar panel count and BTU load before preparing a material list. The tools use metric units with common imperial references where helpful.
- 17 free tools
- Metric + imperial refs
- No registration
- Reference estimates only
Built for global material estimating
Use the calculators as a neutral quantity baseline, then adapt product sizes, local prices, taxes, waste and code requirements to your own country.
No global price ranges
International calculators focus on quantities. When a price field exists, it is for your own local supplier or contractor rate.
Switch by language
Use Spanish, English or French pages depending on the search market and terminology you want to target.
Why we avoid global cost ranges
Construction prices change too much by country, state, city, currency, labor market, tax rules, transport distance and product specification. For global SEO, CalculaObra focuses on what travels well: quantities, formulas, units, waste factors and planning checks.
Costs are local
A slab, wall or roof can have very different prices in the US, New Zealand, the UK, Australia or France. Even regions inside the same country can vary widely.
Quantities are more stable
Area, volume, package count, coverage rate and waste allowance are useful in many markets once the user enters local product sizes.
Local prices stay local
Use the result as a takeoff baseline, then add supplier prices, labor, taxes, delivery and code requirements from your own location.
Start with the most used calculators
These tools cover the first questions most people ask when planning a small construction or renovation job.
Volume and bags
Use it for slabs, pads, footings and rectangular pours when you know length, width and thickness.
Open concrete calculatorConcrete, 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.
Construction estimating basics
Learn material takeoff, units, waste factors and why global price ranges are avoided.
Read guideHow much waste should I add?
Choose practical allowances for cuts, breakage, overlaps and package rounding.
Read guidem² vs m³ and metric units
Understand meters, square meters, cubic meters, centimeters, kilograms and liters.
Read guideProduct coverage rates
Use m²/L, m² per box, kg/m² and useful panel area from the product you will buy.
Read guideHow 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 comparing supplier options, checking package sizes or discussing scope with a contractor.
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.
How many do I need? — most-searched estimators
These are the questions homeowners, DIYers and contractors search most. Each links to a dedicated free calculator with a worked example.
How many bags of concrete do I need?
Enter slab length, width and thickness to get cement bags, sand and gravel for a standard or structural mix — with waste included.
Estimate cement bagsHow many sheets of drywall do I need?
Enter wall length and height to get panel count, screws and joint tape for any stud spacing — 16 in or 24 in OC.
Estimate drywallHow many metal studs do I need?
Calculate studs, top/bottom tracks and panels for light-gauge steel partition walls at standard 16 in or 24 in on-center spacing.
Estimate studsHow many gallons of paint for a room?
Enter room dimensions, number of coats and coverage rate. Doors and windows are deducted automatically. Result shown in gallons and liters.
Estimate paintHow many tile boxes do I need?
Calculate boxes for floors, walls or backsplashes — any tile size. Set waste for straight (10%) or diagonal (15–20%) patterns.
Estimate tileHow much concrete for a slab or patio?
Concrete volume, gravel sub-base and wire mesh for any ground-floor slab — garage, patio, shed or workshop.
Estimate slabWhat 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?
No. The English calculators do not publish country-level market prices or global price ranges. Optional price fields are user-entered local inputs only.
Can I use the calculators in any country?
Yes, for preliminary quantity estimating. Replace prices, bag weights, product dimensions, taxes, labor rates and building code requirements with your local data before purchasing or hiring.
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.
Do the calculators work in feet and inches?
The calculators use metric as the primary unit. Most pages include common imperial equivalents in the guide section — stud spacing in inches (16 in / 24 in on center), drywall panel dimensions in feet (4 ft × 8 ft), concrete in cubic yards and paint in gallons. To convert meters to feet, multiply by 3.281.
How many bags of concrete do I need per cubic yard?
One cubic yard (≈ 0.76 m³) at a standard slab mix (300 kg/m³ cement content) requires approximately 9 bags of 25 kg (55 lb) or 6 bags of 40 kg (88 lb), before waste. Use the Cement Bags Calculator with your exact volume and bag weight.
What waste percentage should I add to my estimate?
Typical allowances: concrete 8%, drywall 10%, tile 10% (straight pattern) or 15–20% (diagonal), laminate flooring 10%, roofing panels 10–15%. Each calculator includes an editable waste field so you can adjust for your specific situation.