Home & Utilities
Home & Utilities tools on UniTools: utility bills from meter readings, heating power and more.
This section is about running a home: bills from meter readings, real water use tap by tap, heating power corrected for climate and insulation, radiator sections, and air conditioner sizing by room volume.
The rest covers the things people usually guess at and get wrong: ventilation rates and duct sizing, the dew point behind misted windows, fertiliser doses from an NPK label, pool volume with its chemistry, and the firewood a season takes.
Tools in this category
Utility Bill Calculator
Works out consumption and cost from meter readings for electricity, water, gas or heating, including two-rate meters, and breaks the result down per day and per person.
Water Consumption Calculator
Works out how much water a household uses per day and per month, splits it across showers, baths, laundry and taps, and shows what it costs.
Heating Power Calculator
Works out the kilowatts of heat a room or a house needs, with corrections for ceiling height, climate, insulation, external walls and windows.
Air Conditioner Sizing Calculator
Works out the cooling capacity a room needs from its volume, sun exposure, occupants and running equipment, and converts it into the usual split-system classes.
Radiator Sections Calculator
Works out how many radiator sections a room needs from its area, ceiling height, climate and the output of a single section.
Ventilation Calculator
Works out the required air flow against three separate norms — by floor area, by occupants and by air changes — and sizes the duct for the flow speed you choose.
Dew Point Calculator
Works out the dew point from air temperature and relative humidity, checks whether a given surface will run with condensation, and gives the humidity limit that keeps it dry.
Fertiliser Calculator
Works out how much fertiliser a plot needs from the nitrogen requirement of the crop and the nitrogen, phosphorus and potassium content of the product.
Pool Volume Calculator
Works out pool volume in cubic metres and litres, the chlorine dose for a target concentration, the pump flow required and the energy to warm the water.
Firewood Calculator
Works out how many stacked cubic metres of firewood a heating season needs, from the floor area, the climate, the species and the efficiency of the stove or boiler.
Underfloor Heating Calculator
Calculates the power, the cable or pipe length and the running cost of an underfloor heating system for a given room.
Water Heater Sizing Calculator
Works out the daily hot water a household uses, the tank volume that covers it and how long the element takes to heat it.
Septic Tank Size Calculator
Calculates the septic tank volume a household needs from the three-day settling rule, and how fast a sealed holding tank would fill.
Stretch Ceiling Cost Calculator
Calculates the area and perimeter of a stretch ceiling and the full cost with the profile, the light cut-outs and the extra corners.
Curtain Fabric Calculator
Works out how many metres of fabric a pair of curtains needs from the rail width, the fullness ratio, the hems and the pattern repeat.
Grass Seed Calculator
Calculates how much grass seed a lawn needs by area and lawn type, for a new sowing or for overseeding an existing one.
Aquarium Volume Calculator
Calculates the real water volume of a tank with the glass, substrate and rim gap subtracted, plus the filled weight and the filter and heater it needs.
Grow Light Calculator
Calculates the grow light wattage a planting area needs from the daily light integral, the photoperiod and the fixture efficacy.
Humidifier Sizing Calculator
Calculates the humidifier output a room needs in grams an hour and the water it will get through in a day.
Snow Load Calculator
Calculates the snow load on a roof from the snow district and the pitch, in kilopascals and kilograms per square metre.
Related categories
FAQs
Does the '100 watts per square metre' rule work?+
As a first approximation, yes — but only at a 2.7 metre ceiling, in a temperate climate, in a building with double glazing. A northern house with old windows wants nearly twice as much.
Why do windows mist up?+
Because the glass is colder than the dew point. At 20 degrees and 60 percent humidity the dew point is 12 — anything colder than that collects condensation.
Size an air conditioner by floor area or by volume?+
By volume. The 'hundred watts per square metre' shorthand assumes a 2.7 metre ceiling and undersizes rooms with high ones.
What is a stacked cubic metre of firewood?+
A cubic metre of stacked logs including the air between them. It holds about 0.65 to 0.7 cubic metres of solid timber.