Engineering lesson
Calculate mixing water after rounding cement sacks
Calculate mixing water from the whole sacks that will actually be mixed. Using the fractional theoretical sack demand understates water for a batch rounded upward.
By PetroCalcHub Team · Updated October 24, 2026 · Free to read and use
Follow the material ledger
The baseline planned slurry is 309.25125 ft³. At 1.32 ft³/sk it requires 234.28125 theoretical sacks. Rounding upward gives 235 whole sacks. At 6.3 US gal/sk, mixing water is 1,480.5 US gal.
The fractional count describes demand, not the selected physical batch. Multiplying 234.28125 by 6.3 would describe a different quantity of dry cement.
Water demand belongs to the recipe
The 6.3 gal/sk value is an explicit synthetic design input. It is not a recommended water addition for every cement blend. Laboratory yield and mixing-water requirement must refer to the same design.
Extra water used for equipment washing, displacement or contingency should appear in a different line. Hiding it inside gal/sk changes the meaning of the recipe input.
Check the prepared volume
The rounded batch produces 235 × 1.32 = 310.2 ft³ at the stated yield, slightly above demand. This overage is due to sack rounding and is distinct from the planned volume excess applied earlier.
If separate slurry designs are mixed in separate batches, round each batch independently and sum their water requirements. One final rounding step is appropriate only for a shared design and batch.
Explore the example
Original synthetic teaching calculation. Equations and fixed controls are stated here; these are not field measurements.
Select one of 5 recorded scenarios. Intermediate states are not interpolated.
Water per sack (US gal/sk) = 6.3. Mixing water (US gal): 1480.5; Whole sacks (sk): 235.
- Mixing water (US gal)
Worked example
Water for the selected whole-sack batch
The baseline volume and yield require 235 whole sacks. Only the assumed mixing-water demand per sack varies.
Relation and unit basis
water = whole sacks × water per sack
Water in US gallons, sacks as an integer count, recipe input in US gal/sk. Service water is excluded.
1. Define the baseline
Water per sack (US gal/sk) = 6.3
The baseline volume and yield require 235 whole sacks. Only the assumed mixing-water demand per sack varies.
2. Select the relation
water = whole sacks × water per sack
Water in US gallons, sacks as an integer count, recipe input in US gal/sk. Service water is excluded.
3. Substitute the values
235 × 6.3 = 1,480.5 US gal
Retain intermediate precision. The displayed values are rounded only after evaluation.
4. Read the result
Mixing water (US gal) = 1480.5; Whole sacks (sk) = 235
Water follows the prepared whole-sack batch, not fractional theoretical demand.
Result and interpretation
Mixing water (US gal) = 1480.5; Whole sacks (sk) = 235
Water follows the prepared whole-sack batch, not fractional theoretical demand.
Change water per sack after the whole-sack count has been fixed. This isolates recipe water demand from geometric volume.
Exact scenario data
Original synthetic teaching calculation. Equations and fixed controls are stated here; these are not field measurements.
| Water per sack (US gal/sk) | Mixing water (US gal) | Whole sacks (sk) |
|---|---|---|
| 5 | 1,175 | 235 |
| 6 | 1,410 | 235 |
| 6.3 | 1,480.5 | 235 |
| 7 | 1,645 | 235 |
| 8 | 1,880 | 235 |
Scroll the table to see all columns. The highlighted row is the worked baseline. Downloads retain full numerical precision.
Test your understanding
Work through the question before revealing its answer. Use the stated assumptions and include units in every numerical step.
1. What water is required for 200 whole sacks at 6.3 US gal/sk?
Show the worked answer
1,260 US gal. Keep wash water and other service volumes outside this mixing-water result.
2. Reproduce the baseline Mixing water (US gal) without rounding intermediate values.
Show the worked answer
235 × 6.3 = 1,480.5 US gal. Mixing water (US gal) = 1480.5. Water follows the prepared whole-sack batch, not fractional theoretical demand.
3. Compare the first and last recorded scenarios. Which input changes?
Show the worked answer
Water per sack (US gal/sk) changes from 5 to 8. Other controls remain as stated in the premise. Mixing water (US gal) changes from 1175 to 1880.
4. What would be needed to apply this example to a different physical system?
Show the worked answer
Replace the synthetic controls with compatible documented inputs and check the relation's assumptions. Water in US gallons, sacks as an integer count, recipe input in US gal/sk. Service water is excluded. Water follows the prepared whole-sack batch, not fractional theoretical demand.
Before using the result
- Round the physical sack count first.
- Use the matching laboratory gal/sk input.
- Separate mixing water from service water.
Water follows the prepared whole-sack batch, not fractional theoretical demand.
Continue learning
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Sources and method
The explanation and synthetic examples are original PetroCalcHub teaching material. The references below support the definitions and model context. They do not supply field validation for the synthetic scenarios.