Construction Tools

Concrete Calculator

Calculate the exact amount of cement, sand, and aggregate for any concrete pour. Supports slabs, footings, columns, round shapes, and steps. Includes material quantities, bag counts, and cost estimates.

Slab / Floor Dimensions

m
m
mm
%
Rs.

Concrete Grade & Mix Ratio Reference

Standard concrete grades and their applications in construction.

Grade Mix Ratio (C:S:A) Strength W/C Ratio Application
M7.5 1:4:8 7.5 MPa 0.60+ Blinding/leveling, non-structural fills
M10 1:3:6 10 MPa 0.55–0.65 Paths, non-structural concrete, blinding
M15 1:2:4 15 MPa 0.50–0.60 Light structures, paths, floor slabs
M20 1:1.5:3 20 MPa 0.45–0.55 Slabs, beams, columns — standard residential RCC
M25 1:1:2 25 MPa 0.40–0.50 Heavy structures, commercial buildings
M30 Design mix 30 MPa 0.35–0.45 Bridges, pre-stressed concrete, high-rise
M35+ Design mix 35+ MPa < 0.40 Bridges, dams, special structures

Concrete Calculation Guide: Mix, Volume & Materials

Accurate concrete calculation is critical to avoid waste, cost overruns, and structural deficiencies. Whether you're building a house foundation, a floor slab, or concrete columns, knowing the exact volume of concrete and the quantities of cement, sand, and aggregate allows you to plan materials, schedule delivery, and control costs before construction begins.

How to Calculate Dry Material Quantities

Concrete volume shrinks when wet — dry materials have voids between particles. The dry volume of materials needed is approximately 1.54× the wet concrete volume (some engineers use 1.57). For a 1:2:3 mix, the total ratio sum is 1+2+3=6 parts. Cement = (1/6) × 1.54 = 0.257 m³ per m³ of concrete = approximately 6.3 × 50kg bags. Sand = (2/6) × 1.54 = 0.513 m³. Aggregate = (3/6) × 1.54 = 0.77 m³.

Concrete Construction Standards in Nepal

Nepal Building Code (NBC) requires a minimum M20 grade concrete for reinforced concrete (RCC) structural elements in residential buildings — slabs, beams, and columns. M15 is acceptable for plain concrete (PCC) blinding layers. The Department of Urban Development and Building Construction (DUDBC) enforces these standards. Post-earthquake construction guidelines (post-2015 Gorkha earthquake) additionally require proper mix design, water-cement ratio control, and minimum 28-day compressive strength testing for structures in seismic zones.

Curing and Quality Control

Proper curing is as important as the mix ratio. Water curing for minimum 7–14 days dramatically increases final strength. In Nepal's hot Terai climate, concrete can dry too fast — cover fresh concrete with wet hessian or polythene sheeting immediately. Never add extra water to concrete after mixing to make it more workable — this raises the water-cement ratio and significantly reduces strength. Use plasticizers (admixtures) instead if workability is needed.

Frequently Asked Questions

To calculate concrete volume: multiply Length × Width × Depth (thickness) to get the volume in cubic units. For example, a 4m × 3m × 0.1m slab = 1.2 cubic meters. Always add 5–10% extra for waste, spillage, and uneven subgrades. Our calculator handles slabs, footings, columns, steps, and round shapes automatically.
The most common mix ratio for general construction is 1:2:3 (1 part cement : 2 parts sand : 3 parts aggregate/gravel) by volume, which gives approximately M20 grade concrete (20 MPa compressive strength). For heavy structural work: 1:1.5:3 (M25). For paths and slabs: 1:2:4 (M15). For foundations in Nepal: M20 is the standard minimum per NBC code.
For a standard 1:2:3 mix: approximately 6.3 bags of 50kg cement per cubic meter of concrete. For 1:1.5:3 mix: about 8 bags per cubic meter. For 1:2:4 mix: about 5 bags per cubic meter. Our calculator shows exact cement bags based on your chosen mix ratio and total concrete volume.
M refers to Mix and the number is the characteristic compressive strength in N/mm² (MPa) after 28 days. M10 (1:3:6): plain concrete, non-structural. M15 (1:2:4): paths, floor slabs, light structures. M20 (1:1.5:3): general RCC slabs, beams, columns — minimum for residential buildings. M25 (1:1:2): heavy structures, commercial buildings. M30+: bridges, high-rise buildings.
Concrete for slab = Length × Width × Thickness. Example: 5m × 4m slab, 150mm thick: 5 × 4 × 0.15 = 3.0 cubic meters. Add 5% waste = 3.15 cubic meters. At 6.3 bags per m³: 3.15 × 6.3 = 20 bags of cement. Multiply cement bags by 2 for sand and by 3 for gravel in a 1:2:3 mix.
1 cubic meter = 35.315 cubic feet. So a 3 cubic meter concrete pour = 3 × 35.315 = 105.94 cubic feet. Ready-mix concrete is typically ordered in cubic meters (m³) in Nepal and India, or cubic yards in the USA (1 cubic yard = 27 cubic feet = 0.765 cubic meters).
Normal weight (reinforced) concrete weighs approximately 2,400 kg per cubic meter (2.4 tonnes/m³). Lightweight concrete: 1,400–1,900 kg/m³. Heavyweight concrete: 3,000–4,000 kg/m³. For structural design, concrete dead load is typically assumed at 24 kN/m³ (2,400 kg/m³). This is important for calculating structural loads on foundations and beams.
Ready-mix concrete (RMC) prices in Nepal vary by grade, location, and supplier. As of recent data, M20 RMC typically costs Rs. 8,000–12,000 per cubic meter in Kathmandu Valley, depending on the plant and delivery distance. M25 costs approximately Rs. 10,000–14,000/m³. Self-mixing on-site is cheaper but less consistent in quality for large volumes.
The water-cement (W/C) ratio critically affects concrete strength. Lower W/C = stronger concrete. Recommended ratios: M15: 0.50–0.60, M20: 0.45–0.55, M25: 0.40–0.50, M30: 0.35–0.45. Never exceed 0.65 for structural concrete. Use only clean, potable water — impurities reduce strength. Reduce W/C further in hot climates where water evaporates quickly.
Concrete reaches approximately 70% of its design strength in 7 days and 99% in 28 days. Minimum curing times: remove formwork from columns and walls after 2–3 days, slabs after 7–14 days (depending on span), beams after 14 days. Always keep concrete moist for at least 7 days by covering with wet burlap or polythene sheeting — this is especially critical in Nepal's hot or dry seasons.
Volume of a cylinder = π × r² × h, where r is radius and h is height. For a 300mm diameter, 3m tall column: r = 0.15m, volume = 3.14159 × 0.15² × 3 = 3.14159 × 0.0225 × 3 = 0.212 m³. For a circular slab with 2m diameter and 150mm thickness: r = 1m, volume = 3.14159 × 1² × 0.15 = 0.471 m³. Our calculator handles all circular shapes automatically.
For 1:2:3 mix per 1 cubic meter of concrete: Cement = 6.3 bags (315 kg), Sand = 0.44 m³ (640 kg approximately), Gravel/Aggregate = 0.88 m³ (1280 kg approximately), Water = 140–160 liters. Dry materials are approximately 30–35% more than wet concrete volume due to voids and compaction. The total dry mix volume ≈ 1.54 × wet concrete volume.