Calculate daily flour yield, village feeding capacity & historical mill production
| Time Period | Grain Ground (lbs) | Flour Yield (lbs) | Loaves of Bread | People Fed |
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Medieval grain milling was the backbone of rural economies from roughly 900–1500 CE. The Domesday Book of 1086 recorded 5,624 watermills in England alone — about one for every 50 households — demonstrating just how central milling was to medieval life. A typical English watermill could grind between 150–400 lbs of grain per hour depending on water flow and stone quality. Millstones were typically 3–5 feet in diameter, made of French burr stone (the finest available) or local sandstone. Lords held monopoly rights called soke, legally compelling villagers to bring their grain to the manorial mill and pay a toll of roughly 1/16th to 1/8th of the grain as multure (milling fee). Windmills appeared in England around 1185–1191 CE and spread rapidly across the flat eastern counties where water was scarce but wind was plentiful.
Select your mill type using the tabs — Windmill, Watermill, or Hand Mill. Each type has historically appropriate inputs: wind speed and sail count for windmills; stream flow rate, wheel diameter and type for watermills; workers and quern type for hand mills. Adjust the sliders and dropdowns to match your scenario, then click "Calculate Mill Output." The tool produces daily, weekly, monthly, and annual figures for grain ground, flour produced, loaves of bread, and people fed.
Understanding medieval mill grain production is essential for historians, reenactors, game designers, students, and anyone building an accurate picture of pre-industrial life. Grain milling was not a minor operation — it was the single most important industrial process in medieval Europe, consuming more engineering effort than any other technology before the steam engine.
Consider a village of 300 people in 14th-century England. Each adult needed roughly 2–2.5 lbs of bread per day, meaning the local mill had to process at least 600 lbs of grain daily just to keep the village fed. A poorly maintained watermill running on a weak stream might barely manage this; a well-positioned overshot mill on a fast river could serve three or four villages. These output calculations determined whether a lord invested in a new millstone, whether a monastery expanded its mill race, or whether a village survived a bad harvest.
For tabletop RPG and strategy game designers, these numbers provide accurate baseline economics for medieval simulation. A kingdom with 50 watermills had a very different food security profile than one relying on 200 windmills.
The calculator uses formulas derived from historical mill survey data, experimental archaeology findings, and primary sources including the Domesday Book and medieval agricultural treatises.
Watermill formula:
Power (hp) = Flow (cfs) × Head (ft) × 0.085 × Efficiency
Grain Rate (lbs/hr) = Power × 150 × Grain Factor
Wheel efficiencies: Undershot 22%, Breastshot 50%, Overshot 75%
Head estimates: Undershot 1.5ft, Breastshot 5ft, Overshot = wheel diameter × 0.9
Grain factors: Wheat 1.0, Rye 1.05, Barley 0.95, Oats 0.88
Windmill formula:
Power (hp) ≈ 0.0015 × Sails × Wind³ (mph)
Grain Rate (lbs/hr) = Power × 120 × Stone Condition × Grain Factor
Hand mill formula:
Base Rate (lbs/hr per worker): Rotary 3, Donkey 8 (2 workers), Lever 15 (4 workers)
Adjusted for grain type and fatigue factor (0.8 after 4 hrs)
Flour yield is calculated as 75% of grain ground (the historical extraction rate for stone-ground wholemeal flour). Bread yield assumes 1.35 lbs of flour per 1 lb loaf (accounting for water addition during baking). Each person requires approximately 1.5 loaves (1.5 lbs) per day.
A well-maintained English watermill of the 12th–14th century could grind between 1,200 and 3,600 lbs (roughly 600–1,600 kg) of grain per day under good conditions, operating 10–14 hours. The best-documented mills, such as those at Toulouse and along the Seine, operated continuously in shifts and could grind 4,000–6,000 lbs per day. Most village mills served communities of 200–500 people and ground considerably less.
Generally no — watermills were more productive and reliable. A good watermill could generate 2–5 mechanical horsepower continuously, while windmills averaged 1–3 hp only when wind conditions were suitable (12–25 mph). However, windmills dominated in flat regions like the Netherlands, East Anglia, and coastal France where water mills weren't viable. The Dutch windmills of the late medieval period became extraordinarily sophisticated and could match or exceed watermill output.
Stone-ground medieval flour was whole-grain by necessity — separating fine white flour from bran required bolting (sieving through fine cloth), a secondary process that cost extra. White "maslin" flour was a luxury. Most bread was brown and dense from whole grain flour. Bran was used as animal feed, particularly for horses and pigs, and was itself a valuable commodity that millers sometimes sold separately after the bolting process.
A mid-sized English watermill operating 12 hours per day could realistically produce enough flour for 800–2,000 people daily, assuming standard medieval bread consumption of about 1.5 lbs per person per day. The Domesday Book's figure of roughly one mill per 50 households suggests historical mills were somewhat undersized relative to community needs, which explains why queuing at the mill was a common source of social conflict in medieval villages.