Civil Engineering

Concrete Mix Design Calculator

Proportion a concrete mix by the absolute volume method. Enter the grade, water-cement ratio, aggregate size, workability and exposure class, and this calculator returns the cement, water, fine aggregate and coarse aggregate required for one cubic metre, together with the mix ratio, the fresh density and the number of cement bags. Durability limits on water-cement ratio and minimum cement content are checked against the exposure class as you go.

IS 10262:2019 · IS 456:2000 Table 5 · absolute volume method

🧲 Mix Inputs

Concrete Grade

Water–Cement Ratio (by mass)

Max Aggregate Size

Workability (Slump)

Exposure Condition (IS 456 Table 5)

Cement Type

Fine Aggregate Fraction (% of total aggregate volume)

Batch Volume (m³)

Per-cubic-metre quantities are unaffected by this; it only scales the batch column.

📊 Mix Proportions

Press Calculate Mix to proportion the mix.

ƒ Governing Formulae

f_m = f_ck + 1.65 · s
C = W / (w/c) subject to C ≥ C_min,exposure
(w/c)_actual = W / C
V_agg = 1 − C/ρ_c − W/1000 − V_air
FA = V_agg · p · ρ_fa
CA = V_agg · (1 − p) · ρ_ca
ρ_fresh = C + W + FA + CA

f_m — target mean compressive strength, MPa

f_ck — characteristic (grade) strength, MPa

s — assumed standard deviation: 4 MPa for M20–M25, 5 MPa for M30 and above (IS 10262 Table 2)

W — free water content, litres per cubic metre, set by aggregate size and slump

C — cement content, kg per cubic metre

w/c — free water–cement ratio by mass

C_min — minimum cement content for the exposure class, IS 456 Table 5

ρ_c — cement particle density: 3150 (OPC), 2900 (PPC), 3200 (SRPC) kg/m³

V_air — entrapped air volume, taken as 0.015 m³ per cubic metre

p — fine aggregate fraction of total aggregate volume

ρ_fa, ρ_ca — saturated surface-dry particle densities, taken as 2650 and 2700 kg/m³

Two assumptions worth knowing. The aggregate particle densities are fixed at 2.65 and 2.70 in this implementation; if your material certificate gives different specific gravities the aggregate masses will shift by roughly the same percentage, though the volumes will not. Entrapped air is taken as a flat 1.5 percent, which suits 20 mm aggregate in non-air-entrained concrete. For air-entrained mixes in freeze–thaw service, the air volume is far larger and this calculation will over-state the aggregate.

📝 Worked Example — M25, Moderate Exposure

Given

M25 concrete, water–cement ratio 0.50, 20 mm maximum aggregate, medium workability (50–100 mm slump), moderate exposure, ordinary Portland cement, fine aggregate 35 percent of total aggregate volume, one cubic metre batch.

Step 1 — target mean strength

M25 falls below M30, so the assumed standard deviation is 4 MPa.
f_m = 25 + 1.65 × 4 = 31.6 MPa

Step 2 — water content

The base water content for 20 mm aggregate is 175 litres per cubic metre. Medium workability needs no correction, so W = 175 L/m³.

Step 3 — cement content and the durability check

C = 175 / 0.50 = 350 kg/m³. Moderate exposure requires at least 320 kg/m³, and 350 clears it, so the entered ratio governs and the actual water–cement ratio stays at 0.500, inside the 0.55 durability limit.

Step 4 — absolute volumes

V_cement = 350 / 3150 = 0.1111 m³
V_water = 175 / 1000 = 0.1750 m³
V_air = 0.0150 m³
V_agg = 1 − 0.1111 − 0.1750 − 0.0150 = 0.6989 m³

Step 5 — aggregate masses

FA = 0.6989 × 0.35 × 2650 = 648 kg/m³
CA = 0.6989 × 0.65 × 2700 = 1227 kg/m³

Cement 350 kg/m³ — 7.0 bags of 50 kg

Water 175 L/m³

Fine aggregate 648 kg/m³

Coarse aggregate 1227 kg/m³

Mix ratio C : FA : CA : W = 1 : 1.85 : 3.50 : 0.50

Fresh density 2400 kg/m³

Target mean strength 31.6 MPa — verdict PASS

These are the calculator's default inputs. Press Calculate Mix without changing anything and you should get exactly these figures back. A fresh density landing on 2400 kg/m³ is a useful sanity check — a normal-weight mix that comes out below about 2300 or above about 2500 usually means the fine aggregate fraction or a specific gravity is wrong.

📏 Inputs, Units and Accepted Ranges

Input	Unit	Accepted	Notes
Concrete grade f_ck	MPa	M20 – M50	Sets the standard deviation used for target mean strength
Water–cement ratio	—	> 0, practically 0.25 – 0.80	Must be greater than zero; very low values leave no room for aggregate and are rejected
Max aggregate size	mm	10, 20, 40	Only these three are offered because they are the only sizes the water table covers
Workability (slump)	mm	25, 75, 150	Discrete bands; intermediate slumps are not interpolated
Exposure condition	—	mild, moderate, severe, very severe	Sets the minimum cement content and the maximum permitted water–cement ratio
Cement type	—	OPC, PPC, SRPC	Changes particle density only, not strength or water demand
Fine aggregate fraction p	%	25 – 50 typical	Fraction of total aggregate volume, not of total mix volume
Batch volume	m³ or yd³	> 0	Scales the batch column only; per-cubic-metre figures do not change

📚 Reference Tables

Durability requirements for normal-weight concrete — IS 456:2000 Table 5

Exposure	Min cement, kg/m³	Max free W/C	Min grade	Typical service
Mild	300	0.65	M20	Protected interior, dry conditions
Moderate	320	0.55	M25	Sheltered exterior, buried, non-aggressive water
Severe	340	0.50	M30	Alternate wetting and drying, seawater splash
Very severe	360	0.45	M35	Seawater tidal zone, aggressive sulphates

Free water content and the corrections applied — IS 10262

Condition	Water, L/m³	Correction applied
20 mm aggregate, medium slump (base case)	175	none
10 mm aggregate	190	+15
40 mm aggregate	160	−15
Stiff, 10–25 mm slump	−	−15
High, 100–175 mm slump	−	+20

Corrections are cumulative. A 10 mm aggregate mix at high slump takes 175 + 15 + 20 = 210 L/m³.

Particle densities used in the absolute volume calculation

Material	Density, kg/m³	Specific gravity
OPC 43 / 53 grade cement	3150	3.15
PPC / blended cement	2900	2.90
Sulphate-resisting Portland cement	3200	3.20
Fine aggregate (natural sand, SSD)	2650	2.65
Coarse aggregate (crushed stone, SSD)	2700	2.70
Water	1000	1.00

Indicative cement content by grade — 20 mm aggregate, medium slump, moderate exposure

Grade	Std deviation s, MPa	Target mean f_m, MPa	Typical W/C	Cement, kg/m³	50 kg bags
M20	4	26.6	0.55	320	6.4
M25	4	31.6	0.50	350	7.0
M30	5	38.3	0.45	389	7.8
M35	5	43.3	0.42	417	8.3
M40	5	48.3	0.40	438	8.8

Cement figures follow from C = 175 / (w/c) at the tabulated ratio, then the moderate-exposure floor of 320 kg/m³. Run the calculator for your own exposure class rather than reading these off directly.

❓ Frequently Asked Questions

How do you calculate a concrete mix design as per IS 10262?

You fix the water content from the maximum aggregate size and the required workability, divide it by the chosen water-cement ratio to get the cement content, then raise that cement content if it falls below the durability minimum for the exposure class. The remaining volume in one cubic metre, after subtracting the volumes of cement, water and entrapped air, is filled with fine and coarse aggregate in the proportion you select. That last step is the absolute volume method and it is what this calculator performs.

What is the difference between nominal mix and design mix concrete?

A nominal mix uses fixed volumetric proportions such as 1:1.5:3 for M20, taken straight from a table without regard to the specific materials. A design mix is proportioned by calculation from the target mean strength, the actual water demand of the aggregates and the durability limits for the exposure condition. IS 456 restricts nominal mixes to M20 and below; anything above that must be a design mix.

Why is my actual water-cement ratio lower than the value I entered?

Because the durability minimum cement content overrode your input. If the water content divided by your entered ratio produces less cement than the exposure class permits, the cement is raised to that minimum while the water stays fixed, so the actual ratio drops. The calculator reports the actual ratio rather than the one you typed, because that is the value the concrete will be built to.

How many bags of cement are needed for 1 cubic metre of M25 concrete?

For a typical M25 mix at a water-cement ratio of 0.50 with 20 mm aggregate and medium workability, the cement content works out at 350 kg per cubic metre, which is 7.0 bags of 50 kg. This figure moves with the water-cement ratio, the aggregate size and the exposure class, so it should be read from the calculation rather than assumed.

What is target mean strength and why is it higher than the grade?

Target mean strength is the average strength the mix must be proportioned for so that the characteristic strength is still met after normal production variability. It equals the characteristic strength plus 1.65 times the standard deviation, the factor 1.65 corresponding to a 5 percent failure rate. IS 10262 assumes a standard deviation of 4 MPa for M20 and M25 and 5 MPa for M30 and above.

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Concrete Mix Design Calculator — multicalci.com. Results are indicative and follow IS 10262 and IS 456 with the stated assumptions. Trial mixes and cube tests remain mandatory before any mix is used in construction.