About

ToolboxCalc works out quantities and code checks for building, electrical and garden jobs — concrete, aggregate, mulch and asphalt; wire size, voltage drop, conduit and box fill; grass seed, sod, fertilizer, soil and plant counts. It brings together three earlier sites: Builder’s Calculator, Electrician’s Calculator and Gardener’s Calculator.

Where the numbers come from

Building materials. Bag yields are the figures manufacturers print on the bag: 0.60 ft³ for an 80 lb bag of standard pre-mixed concrete, 0.45 ft³ for a 60 lb bag. Material densities are standard industry planning figures, shown on every page that uses one. Code references — footing widths, riser heights, slab thicknesses — are cited to the International Residential Code where they come from it.

Electrical. The calculators hold the NEC tables so you do not have to look them up: Chapter 9 Table 8 for conductor resistance, Table 310.16 for ampacity at 30°C with not more than three current-carrying conductors, Chapter 9 Tables 4 and 5 for conduit and conductor areas, Chapter 9 Table 1 for fill limits (53% for one conductor, 31% for two, 40% for three or more), Table 314.16 for box fill, and 240.4(D) for the small-conductor overcurrent limits. Ambient and bundling derating are not applied.

Lawn and garden. Seeding rates are the commonly published cooperative-extension ranges, in pounds per 1,000 square feet. Fertilizer is worked from the N-P-K analysis on the bag rather than a coverage claim. Plant spacing uses square and triangular packing, where a staggered layout fits about 15% more plants at the same spacing.

Corrections made along the way

The earlier gardening calculator had a unit-conversion fault that made every area-based answer about 10.8 times too low; the earlier electrical calculator reported a 52.5% conduit fill with no warning that it exceeded the 40% limit. Both are fixed, and the test suites cover those specific cases.

What these estimates are not

They are planning and purchasing estimates. They are not structural engineering, not agronomic advice, not an electrical design or inspection, and not a substitute for your local code or the label on the product you buy.

Corrections

If a figure here looks wrong, it may well be. Send a note through the contact page saying which page and which number.