Methodology
How the calculators work
Every calculator follows the same rules, so a result from one tool can be compared with another. Each calculator page also lists its own formula, assumptions and a worked example.
Units
Calculations use metric units internally: metres and centimetres for length, square metres for area, litres or cubic metres for volume, and grams or kilograms for mass. Imperial conversions use the exact factors published by NIST (1 yard = 0.9144 m, 1 lb = 0.45359237 kg, 1 oz = 28.349523 g). One millimetre of water over one square metre is one litre.
Defaults are examples
Pre-filled values — a coverage rate, a portion size, a bag yield — are examples so that the page shows a complete calculation. They are not recommendations. Replace them with the figure on your product label, recipe or supplier quote; that figure always takes precedence.
Allowances and rounding
- An allowance for waste, cuts or settling is applied once, as a percentage of the measured quantity, before rounding.
- Only the final purchase quantity is rounded, and it is rounded up to whole packs, bags, rolls or tins. A requirement that exactly matches a pack size (for example 2.5 L of paint with 2.5 L tins) is not rounded up to an extra pack.
- When materials are sold separately (soil and compost, or several recipe ingredients), each is rounded to its own packs, because surplus of one cannot replace another.
- Conservative counts are labelled as such, for example a drywall layout count that does not assume offcuts are reused.
Validation
Inputs outside a sensible range, impossible combinations (openings larger than the wall, a piece wider than the fabric, a discount above 100%) and incompatible units (comparing a price per kilogram with a price per litre) are rejected with a message instead of producing a misleading number.
Testing
Each calculation mode is covered by automated tests that compare the engine with examples calculated independently, including exact pack boundaries, unit conversions and invalid inputs. The worked examples shown on calculator pages are generated by the same code as the calculators.
Limits
The calculators estimate quantities. They do not design structures, set food-safety times, choose insulation performance, or replace product instructions and qualified advice. Where safety matters, the relevant page says so and links to an authoritative source.
Changes and corrections
When a method changes, the calculator page is updated. Report a suspected error through the contact page, with the page address and the values you entered.
What is Babushka Market for?
Babushka Market helps plan quantities and purchases for cooking, home projects, gardens, crafts, parties and shopping. Its calculators show the inputs and assumptions behind a result. They do not inspect your materials or circumstances, so compare the output with product instructions and the measurements you actually have.
Worked planning example
Yes. The moving-box example divides each contents volume by its box capacity and rounds after a 10% allowance: 11 small, 15 medium and eight large boxes. Check the displayed formula and pack rounding, then replace the example measurements and rates with your own inputs.
What does Babushka Market calculate?
Babushka Market helps plan quantities and purchases for cooking, home projects, gardens, crafts, parties and shopping. Its calculators show the inputs and assumptions behind a result. They do not inspect your materials or circumstances, so compare the output with product instructions and the measurements you actually have.
Can I check a result before buying?
Yes. The moving-box example divides each contents volume by its box capacity and rounds after a 10% allowance: 11 small, 15 medium and eight large boxes. Check the displayed formula and pack rounding, then replace the example measurements and rates with your own inputs.
Calculation/content reviewed 4 October 2026. Source: Babushka Market’s displayed formulas, units and labelled editable assumptions. How the estimates work