10 lb (4.536 kg) of grain, mashed at a typical 1.5 qt/lb ratio and targeting a 152°F (66.7°C) mash from 68°F (20°C) grain, needs 14.2 L of strike water at 72.9°C. Reproduce this exactly, or adjust the ratio and target for your own recipe.
Strike water isn't your only water number
The strike water figure above is what goes into the mash tun to hit your target temperature — it is not the same as your total pre-boil volume, because a meaningful amount of that water never leaves the grain bed. Grain absorbs roughly 1.04 L of water per kg, John Palmer's published 0.5 qt/lb figure — for this 4.536 kg grain bill, that's roughly 4.7 L absorbed and never collected as runnings, regardless of how thoroughly you sparge. See how much water do my grains absorb for where that figure comes from and how it scales with a larger or smaller grain bill.
Putting it together for a full brew day
If you're batch- or fly-sparging rather than doing a single-infusion no-sparge mash, your total water for the day is strike water plus sparge water, and your total pre-boil kettle volume is that combined figure minus what the grain absorbed. A rough planning sequence: decide your target pre-boil kettle volume first (based on your batch size, boil-off rate, and any dead space in your system), add back the grain absorption figure to get your total water needed, then split that total between strike water (calculated here, driven by your target mash temperature and ratio) and sparge water (the remainder, added during lautering).
Why the strike figure alone understates what you'll actually use
A brewer who plans only the strike-water volume and assumes that's the whole day's water requirement typically ends up short of their target pre-boil volume by roughly the grain-absorption figure — a modest shortfall at 10 lb of grain, but one that compounds on bigger grain bills. If you're scaling this recipe up or down, both the strike-water volume and the absorption figure scale together with grain weight, while the strike temperature itself barely moves — see the malt reference for typical grain-bill weights across common batch sizes.
A cooler-specific consideration
An insulated cooler mash tun introduces one more variable this calculation doesn't account for: the cooler's own plastic or metal has to warm up too, quietly stealing some of the strike water's heat before the grain ever gets a chance to. How to hit mash temperature in a cooler covers the preheat routine that neutralises this, so your actual result matches the number calculated here rather than landing a degree or two short.