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Calculators & Tools

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Work It Out First

Calculators & tools

The measurements worth getting right before you buy anything — how much seed, how many bags, what size unit, how long to run a zone. Every calculator shows the formula it uses and cites where the numbers come from.

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Lawn

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Lawn Area Calculator Work out the square footage of a lawn from simple measurements, including L-shapes and circular beds — the number every seed, fertilizer and mulch calculation starts from. Grass Seed Calculator How many pounds of grass seed you need, by species and by whether you are seeding bare ground or overseeding an existing lawn. Lawn Fertilizer Calculator How many pounds of a given fertilizer to apply, worked from its nitrogen percentage and your target rate — the calculation the bag label leaves you to do.

Garden

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Mulch Calculator How much mulch you need in cubic yards and in bags, from bed area and the depth you want — plus the point at which bulk delivery beats buying bags. Raised Bed Soil Calculator How much soil to fill a raised bed, in cubic feet, cubic yards and bags — with a suggested mix ratio for beds you intend to grow food in.

Home

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Paint Calculator How many gallons of paint a room needs, accounting for doors, windows and the number of coats — the calculation that decides whether you make a second trip. BTU Calculator What cooling capacity a room needs in BTUs, adjusted for sun, occupancy and kitchens — and why an oversized unit cools worse, not better. Air Purifier Size Calculator The CADR rating a room actually needs, using AHAM's two-thirds rule, plus what air changes per hour you will get — the two numbers that matter more than the room size printed on the box.

Watering & irrigation

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Water Flow Rate & Pressure Test Measure your real available flow in gallons per minute with a bucket and a stopwatch — the single number every sprinkler, drip and hose decision depends on. Sprinkler Run Time Calculator How many minutes to run each sprinkler zone, worked from your measured precipitation rate and how much water the lawn actually needs that week. Hose Pressure Loss Calculator How much pressure a garden hose loses over its length, by diameter and flow rate — and why a longer or narrower hose ruins a sprinkler. Sprinkler Zone Capacity Calculator How many sprinkler heads or drip emitters one zone can run on your available flow — the calculation that decides how many zones a system needs.

Running costs

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Appliance Running Cost Calculator What any appliance costs to run per day, month and year, from its wattage and your electricity rate — the number that decides whether the cheap model was actually cheap. Heating Cost Comparison Calculator What it costs to deliver the same heat with a heat pump, gas, propane, oil or electric resistance — the only fair way to compare fuels priced in different units. Repair or Replace Calculator Whether to fix an appliance or buy a new one, weighing the quote against replacement price, the age of the unit and how much life it has left. Irrigation Water Cost Calculator What it costs to water a lawn for a season, from area, watering depth and your water rate — and what switching to drip or cutting one day a week would save. Generator Runtime Calculator How long a generator runs on a tank at your actual load, how much fuel an outage will take, and what it costs per day. Standby Power Calculator What the devices in your house cost while switched off — the always-on load that runs 8,760 hours a year and never appears as a line on any bill.

Why these show their working

A calculator that produces a number from nowhere is asking for exactly the blind trust this site refuses to ask for anywhere else. So each one states its formula in plain language and links the standard or extension guidance it follows — AHAM’s two-thirds rule for air purifier sizing, Department of Energy figures for cooling capacity, university extension rates for seed and fertilizer. Where a figure is a rule of thumb rather than a standard, we say so, and say what shifts it.