How do I calculate the capacity of a flour mill I need?

Start from your finished flour sales per day, divide by the extraction rate (typically 0.72–0.78) to get wheat intake, then add 10% headroom for peak days and cleaning losses. A mill selling 15 t of flour per day at 75% extraction needs 20 t of wheat per day, so a 20–25 t/d plant is correct.

Is it better to buy a larger plant than I need now?

Usually yes, up to one capacity step. The marginal capital cost of the next size up is typically 15–25%, while the cost of a second plant later is 100% plus a building extension. But do not jump two steps — an oversized plant runs below its design point where specific power consumption rises.

What determines the number of roll passages?

Target extraction and flour grade count. 3B2M is the minimum for a clean patent flour; 4B4M allows two or three grades simultaneously; 4B5M1S1T with a purifier is required for genuinely low-ash patent flour at high extraction.

How much building height does a flour mill need?

Below 30 t/d with floor-mounted plansifters: 4–6.5 m clear. At 40–60 t/d: 8 m. Above 60 t/d the plant is normally storey-typed with 12.5–27.5 m total height depending on capacity.

How long does it take to build a flour mill?

A 20–30 t/d plant: 80–100 days from order to first flour. A 60 t/d plant: 100–130 days. A 300 t/d turnkey plant: 8–11 months including civil works.

Pillar handbook

How to Size a Wheat Flour Mill: The Complete Engineering Method

A step-by-step method for sizing a wheat flour milling plant — from demand analysis and extraction rate through flow sheet passages, sifter area, power budget and building dimensions. Includes worked examples for 20, 60 and 200 t/d plants.

By Haiyun engineering desk Updated 2026-11-07 22 min read

Key takeaways

Size from finished flour demand backwards, not from wheat intake forwards — the difference between 72% and 78% extraction is 8% of your wheat bill.
Sifter area is the binding constraint in most flow sheets: allow 1 m² per 0.8 t of daily capacity for a 4B5M layout.
Power consumption per tonne falls from ~72 kWh at 60 t/d to ~67 kWh at 500 t/d; at 300 t/d that gap is worth roughly 500,000 kWh a year.
A 30 t/d plant needs 18 × 6 × 6.5 m and 92 kW; a 200 t/d plant needs 50 × 7.5 × 22.5 m and 690 kW. Those numbers decide the building before the machines.

Sizing a flour mill is an exercise in working backwards. Almost every failed project we are asked to rescue was sized forwards — someone decided to buy a 30 t/d plant, built a building around it, and only later worked out that the local market could absorb 12 t of flour a day.

The method below is the one we use on every enquiry. It has five stages, and each stage constrains the next.

Stage 1 — Establish finished flour demand, not wheat intake

The first number you need is not tonnage. It is bags sold per day, by grade.

Write it down like this:

Grade	Bag size	Bags/day	Tonnes/day	Price/t
Patent / special grade 1	25 kg	300	7.5	reference
Standard / grade 2	50 kg	140	7.0	−12%
Bran (by-product)	50 kg	120	6.0	−70%

This table does three things at once. It gives you total flour output (14.5 t/day), it gives you the product mix that determines how many passages and sifter compartments you need, and it gives you the revenue structure that determines whether the plant can service its capital.

Most feasibility studies skip this and go straight to “we want a 30-ton plant”. That is buying a machine before knowing the job.

Stage 2 — Convert flour demand into wheat intake

Extraction rate is the ratio of flour produced to wheat milled. It is the single most economically important number in the plant, because wheat is 65–80% of your cost base.

Product	Typical extraction	Wheat needed per tonne of flour
Patent flour only	65–72%	1.39–1.54 t
Patent + standard (2 grades)	75–78%	1.28–1.33 t
Atta / whole wheat	85–92%	1.09–1.18 t
Maida (South Asian)	72–76%	1.32–1.39 t

At 14.5 t of flour per day and 76% extraction, you need 19.1 t of wheat per day. Add 8% for cleaning losses, moisture shrinkage in tempering and spillage: 20.6 t/day.

Now add headroom. A plant that runs at 100% of design capacity every day has no maintenance window and no ability to catch up after a breakdown. Design for 85–90% utilisation:

20.6 ÷ 0.87 ≈ 23.7 t/day → specify a 25 t/d plant.

This is why so many buyers end up on the 6FTDP-25 rather than the 20. They started with a “20 t/d requirement” and the arithmetic moved them one step.

Assumptions matter here. If your wheat is dirty (2.5% impurity instead of 1%), cleaning losses double and you need a bigger intake for the same output. If your wheat is dry (10.5% moisture instead of 12.5%), you lose less in tempering but the bran is more brittle and extraction drops. Both effects are real and both are usually ignored at the enquiry stage.

Stage 3 — Choose the flow sheet, which sets the passage count

The flow sheet is the diagram of how wheat becomes flour. Its notation is compact: 3B2M means three break passages and two reduction passages.

Flow sheet	Minimum capacity	Grades produced	Purifier	Typical extraction
3B2M	15 t/d	1–2	No	72–74%
3B3M	25 t/d	2	No	74–76%
3B4M1S	40 t/d	3	Yes (1 unit)	75–77%
4B5M1S1T	60 t/d	3–4	Yes (bank)	76–79%
5B7M2S2T	100 t/d+	4+	Yes (bank)	77–80%

B = break, M = reduction, S = scratch/sizing, T = tailing.

Here is the rule that matters: you cannot reach a given extraction with too few passages. Each additional break passage scrapes a little more endosperm off the bran. Each additional reduction passage grinds that endosperm a little finer. Stop too early and you leave flour on the bran, which goes out the door as low-value by-product.

A 3B2M plant physically cannot exceed about 74% extraction no matter how it is operated. If your business plan assumes 78%, you need 4B4M and a purifier. This is the most common arithmetic error in small-mill feasibility.

Stage 4 — Size the sifting area, which usually binds

Sifting area is the constraint that surprises people, because it is invisible on a price list. Sifters are expensive and large, and under-sizing them produces a plant that grinds fine but cannot classify.

The working rule for a standard flow sheet:

Sifting area (m²) = daily capacity (t/d) ÷ 0.8

So:

Capacity	Sifter area needed	Typical configuration
20 t/d	25 m²	2 × twin-bin plansifter (5 m² each bin)
30 t/d	37.5 m²	2 × twin-bin, or 1 high square FSFG4×24
60 t/d	75 m²	2 × FSFG6×24 (39.5 m² each)
100 t/d	125 m²	FSFG8×24 + FSFG6×24, or 3 × FSFG6×24
200 t/d	250 m²	Bank of 4–5 high square units
300 t/d	375 m²	Bank of 7–8 high square units

The rule assumes a standard 4B5M flow sheet. If your flow sheet has more passages, you need more sifting area. If you are making a single whole wheat product with no grading, you need much less.

Stage 5 — Set the power budget and the building envelope

Power and building dimensions both flow directly from capacity, and both are published in our plant tables because they are the two numbers that block a project at the planning-permission stage rather than the purchase stage.

Capacity	Installed power	kWh per tonne flour	Building (L × W × H)
30 t/d	92 kW	70–74	18 × 6 × 6.5 m
60 t/d	150 kW	70–74	24 × 8 × 8 m
100 t/d	308 kW	70–74	35 × 7.5 × 18.5 m
200 t/d	690 kW	65–71	50 × 7.5 × 22.5 m
300 t/d	920 kW	65–71	60 × 11 × 27.5 m
500 t/d	1,650 kW	65–70	55 × 17 × 27.5 m

Two observations that are worth more than the table.

First, specific power falls with scale. The gap between 74 and 65 kWh/t looks small until you multiply it. A 300 t/d plant running 330 days consumes 300 × 330 × 7 = 693,000 kWh a year more if it operates at 72 instead of 65 kWh/t. At USD 0.10/kWh that is USD 69,300 per year, every year, for the life of the plant. Scale is not just about labour.

Second, height is the expensive dimension. Going from 8 m to 18.5 m roughly doubles civil cost per square metre. This is why the 20–30 t/d class uses floor-mounted plansifters — it keeps the building cheap. Above 60 t/d the gravity flow advantage of a tower pays for the structure within a few years of reduced pneumatic conveying power.

Worked example — a 60 t/d plant in East Africa

A buyer has a wheat supply contract and a market for two flour grades.

Demand: 45 t/day of patent flour, 15 t/day of standard flour. Total 60 t/day.
Extraction: 78% at two grades. Wheat needed = 60 ÷ 0.78 = 76.9 t/day. Plus 6% losses = 81.5 t/day.
Flow sheet: 4B5M1S1T with two high square plansifters and a purifier bank. This is the minimum that reaches 78%.
Sifter area: 60 ÷ 0.8 = 75 m². Two FSFG6×24 units give 79 m². Correct.
Power: 150 kW installed, 72 kWh/t. Daily consumption 4,320 kWh.
Building: 24 × 8 × 8 m, storey-typed with two floors.

The entire sizing exercise took six numbers. The rest of the project — civil design, electrical, erection sequencing — is engineering labour, but it is labour applied to a correctly specified target.

Where sizing goes wrong

Four failure modes, in order of frequency:

Sizing to peak demand instead of average. A mill that sells 20 t/day in December and 8 t/day in June should not buy a 20 t/d plant. It should buy 12 t/d and run an extra shift in December.

Ignoring wheat variability. A plant specified for 12.5% moisture hard wheat will underperform on 10.5% soft wheat. Specify the worst wheat you will actually buy, not the best.

Under-sizing sifting to save capital. Sifter cost is roughly 12–18% of plant cost. Cutting it by a third saves 4–6% of capex and costs 3–5 points of extraction forever.

Forgetting the by-product. Bran is 22–28% of intake and it has to go somewhere — storage, bagging, transport. A 60 t/d plant produces 18 t/day of bran, which needs a silo or a very reliable buyer.

What to send us

If you want a flow sheet rather than a brochure, send:

Target flour output per day, by grade
Wheat type, origin and typical analysis (moisture, protein, ash, impurity)
Available building footprint and height, or confirmation that a new building is possible
Local power supply: voltage, phases, available kVA
Water availability and effluent constraints
Labour availability and skill level
Budget range and financing structure

With those seven items we can produce a preliminary flow sheet, equipment list and budget range in 12 working hours. Without them, any quotation you receive is a guess dressed as a price.

Articles in this handbook