How do you convert quarts per pound to liters per kilogram?
Multiply by 2.086. A US quart is 0.946 L and a pound is 0.4536 kg, so 1 qt/lb = 0.946 ÷ 0.4536 = 2.09 L/kg: 1.25 qt/lb is 2.6 L/kg, 1.5 is 3.1, and the metric brewer's round 3.0 L/kg is 1.44 qt/lb. Worth stating plainly because one of the most-read pages on the subject gives the factor as 2.336 — convert a 1.5 qt/lb recipe with that and you'll mash 12% wetter than its author did. Not fatal, but not what you meant.
Strike water = grain weight × thickness · 11 lb × 1.5 qt/lb = 16.5 qt = 4.1 gal · 5 kg × 3.13 L/kg = 15.6 L
Strike water by grain bill and thickness
Water into the mash tun (add your tun's deadspace on top):
| Grain | Thickness, qt/lb (L/kg) | ||||
|---|---|---|---|---|---|
| 1.00 (2.1) | 1.25 (2.6) | 1.50 (3.1) | 1.75 (3.7) | 2.00 (4.2) | |
| 8 lb · 3.6 kg | 2.00 gal · 7.6 L | 2.50 gal · 9.5 L | 3.00 gal · 11.4 L | 3.50 gal · 13.2 L | 4.00 gal · 15.1 L |
| 10 lb · 4.5 kg | 2.50 gal · 9.5 L | 3.13 gal · 11.8 L | 3.75 gal · 14.2 L | 4.38 gal · 16.6 L | 5.00 gal · 18.9 L |
| 12 lb · 5.4 kg | 3.00 gal · 11.4 L | 3.75 gal · 14.2 L | 4.50 gal · 17.0 L | 5.25 gal · 19.9 L | 6.00 gal · 22.7 L |
| 14 lb · 6.4 kg | 3.50 gal · 13.2 L | 4.38 gal · 16.6 L | 5.25 gal · 19.9 L | 6.13 gal · 23.2 L | 7.00 gal · 26.5 L |
| 16 lb · 7.3 kg | 4.00 gal · 15.1 L | 5.00 gal · 18.9 L | 6.00 gal · 22.7 L | 7.00 gal · 26.5 L | 8.00 gal · 30.3 L |
| 18 lb · 8.2 kg | 4.50 gal · 17.0 L | 5.63 gal · 21.3 L | 6.75 gal · 25.6 L | 7.88 gal · 29.8 L | 9.00 gal · 34.1 L |
| 20 lb · 9.1 kg | 5.00 gal · 18.9 L | 6.25 gal · 23.7 L | 7.50 gal · 28.4 L | 8.75 gal · 33.1 L | 10.00 gal · 37.9 L |
Water only. The mash occupies roughly 0.32 qt (0.67 L) more per lb (kg) of grain than the water alone — see the tun check.
Will it fit in the tun?
Crushed grain displaces about 0.32 qt per pound (0.67 L per kg) on top of the water it sits in. Eleven pounds at 1.5 qt/lb is 4.1 gal of water but about 5.0 gal of mash. Run that backwards and a 10-gallon cooler holds about 22 lb at 1.5 qt/lb or 25 lb at 1.25 — the reason big beers get mashed thick, and why "thick" is a capacity decision more often than a flavor one. A 35 L all-in-one mashes about 9.5 kg at 3 L/kg but only 5.2 kg full-volume at 6 L/kg; past that, you hold some water back and sparge. The calculator's tun field does this arithmetic for your numbers.
What does mash thickness actually change?
Less than the arguments about it suggest. Across the normal 1–2 qt/lb (2–4 L/kg) range the effect on wort fermentability is under 5% (Palmer, 2017, cited by Grainfather): a thinner mash lets the enzymes move a little more freely and finishes a touch drier; a thicker one protects them slightly better at high temperatures and holds its heat better in a cooler. Beyond that, thin mashes run off faster and rinse better, thick ones make a stronger first wort and are gentler on a tun that's nearly full. Two things do change materially with thickness: mash pH — more water from an alkaline supply raises it, so full-volume brewers with pale grists lean on acid — and the strike temperature, which the thickness sets directly.
If you batch sparge from a cooler, 1.25–1.5 qt/lb keeps the mash warm and the sparge volume sensible. If you brew in a bag or an all-in-one, the "thickness" is just the total water divided by the grain, and the beer doesn't mind. If you're chasing body or dryness, mash temperature and the grain bill move it ten times as far as thickness does. Set the ratio once in your profile, let the strike and water calculators use it, and spend the attention elsewhere.
Under about 1 qt/lb (2.1 L/kg) the mash turns to porridge: dough balls that never wet through, a runoff that sticks, and enzymes that have to work in syrup. If your tun forces you there for a big beer, take some of the fermentables as extract or sugar in the kettle instead, or split the mash. Above 3.5 qt/lb (7 L/kg) nothing breaks — conversion just takes a bit longer and the pH wants watching.