Civil Engineering Calculators
Free online calculators for site and design engineers — lap length, bar bending schedule, beam analysis, concrete mix design, retaining walls and more. Every formula is referenced to the Indian Standard it comes from.
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Quick calculators
Instant answers for everyday site questions. Results update as you type.
Formula: weight = D²/162 kg per metre (steel density 7850 kg/m³). Need a full schedule? Use the BBS Generator.
Dry volume factor 1.54, cement 1440 kg/m³, 50 kg bags. For M25 and above use a design mix — try the IS 10262 mix design tool.
Simply supported, elastic, gross section (I = bD³/12). Cracked RCC sections deflect more. For other supports and loads use the Beam Analysis Calculator.
Handy site values: 1 kN = 101.97 kgf · 1 N/mm² = 1 MPa = 10.197 kgf/cm² · 1 m³ = 35.315 ft³ · 1 sq m = 10.764 sq ft.
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Excel toolkits for site engineers
Same formulas, ready to print and share with your team — no internet needed on site.
Civil Site Engineer Bundle₹299 
Building Estimate & BOQ Excel Kit₹299 
RCC Lap Length Calculator & Field Guide₹199 Learn the formulas behind the tools
Frequently asked questions
Are these civil engineering calculators free?
Yes. Every calculator on this page and the linked tool pages is free to use without signing up. Pro members can additionally export calculator reports and download the Excel toolkits.
How is the weight of a steel bar calculated?
Weight per metre of a round bar = D² / 162 kg/m, where D is the bar diameter in mm. It comes from the density of steel (7850 kg/m³). Example: a 12 mm bar weighs 144 / 162 = 0.889 kg/m, so a 12 m bar weighs about 10.7 kg.
How many cement bags are needed for 1 m³ of M20 concrete?
For nominal mix M20 (1 : 1.5 : 3), dry volume = 1.54 m³. Cement = 1.54 × 1/5.5 = 0.28 m³ × 1440 kg/m³ ≈ 403 kg, which is about 8 bags of 50 kg. Sand ≈ 0.42 m³ and coarse aggregate ≈ 0.84 m³. Grades M25 and above should be designed as per IS 10262.
What is the bending moment of a simply supported beam with UDL?
Maximum bending moment = wL² / 8 at mid-span, maximum shear = wL / 2 at the supports, and maximum deflection = 5wL⁴ / (384EI). A common serviceability limit for RCC beams is span / 250 (IS 456 Cl. 23.2).
Can I use these results for real construction?
The tools follow IS-code formulas and are meant for learning, quick checks and estimates. For actual design and construction, verify results against the current code and have the work checked by a qualified structural engineer.
Results are for education and quick checks. Verify critical designs with the current IS code and a licensed engineer.