Free DIY calculators for your home
Work it out yourself before you buy or build.
HomeSums gives you simple, honest tools for the numbers behind home projects: running costs, replacing appliances, damp and off-grid power. No sign-up, no sales pitch, and every formula shown.
Example result · Replace or Keep
Older fridge-freezer vs efficient model
450 kWh vs 200 kWh a year at €0.30 per kWh, €700 purchase price.
The tools
Pick a tool to get started
Each tool does one job well, explains how it works and shows a worked example, so you can check every number.
Energy & Bills
Running costs, heating and radiators.
Electricity Cost Calculator
Find out what your appliances cost to run per day, month and year.
Replace or Keep
Compare an old appliance with a replacement and see the payback time.
Heating Cost Compare
Compare what it costs to heat a room with gas, oil, electric heaters, storage heaters or a heat pump.
Radiator & BTU Calculator
Work out what size radiator a room needs, in watts and BTU, for a boiler or a heat pump.
Heat Loss Calculator
Estimate your whole home's heat loss, the heat pump size it needs and what heating costs a year.
EV Charging Cost
See what an electric car costs to charge per mile, per charge and per year, and the saving over petrol.
U-Value Calculator
Build up a wall, loft, roof or floor layer by layer to see its U-value and what its heat loss costs.
Damp & Air
Condensation, mould and dehumidifiers.
Dehumidifier Picker
Find the right dehumidifier size and type for your room.
Damp & Mould Check
Check whether a window or wall will get condensation or mould, and what humidity keeps it dry.
Solar & Off-Grid
Solar panels, off-grid power and 12 V wiring.
Off-Grid Planner
Size the battery, solar panels and inverter for a cabin, van or boat.
Plug-in Solar Payback
See what a balcony solar kit would save and how many years it takes to pay back.
Solar Panel Calculator
See what solar panels on your roof would make and save, and how many years they take to pay back.
Cable Size Calculator
Work out the cable size and fuse for a 12 V, 24 V or 48 V circuit in a van, boat or off-grid system.
DIY & Materials
How much to buy for your next project.
Paint Calculator
Work out how much paint a room or the outside of a house needs, and which tins to buy.
Concrete Calculator
Work out the concrete for a slab, footing, fence posts or steps, and the cement, ballast or bags to buy.
Tile Calculator
Work out how many tiles, boxes, adhesive and grout a floor or wall needs.
Wallpaper Calculator
Work out how many rolls of wallpaper a room or feature wall needs, allowing for the pattern repeat.
Square Metre Calculator
Work out the area of a room, floor or garden in m² and ft², including L-shapes and circles.
Gravel Calculator
Work out the tonnes and bags of gravel, chippings or sub-base for a path, border or driveway.
Decking Calculator
Work out the deck boards, joists and screws or clips for a timber or composite deck.
Flooring Calculator
Work out the packs of laminate, wood or click vinyl flooring a room needs, with underlay and beading.
Home & Living
Everyday jobs around the home.
Laundry Symbols
Tap the symbols on a care label to see what they mean and the wash, dry and iron settings to use.
Curtain Size Calculator
Work out the pole length, curtain width and drop, the ready-made size to buy and the fabric to make them.
TV Size Calculator
Find the best TV size for where you sit, or the best seat for your TV, and how high to mount it.
Light Bulb Finder
Find the fitting, brightness and colour of the LED to replace any bulb, and keep a list of your bulbs.
Why HomeSums
Built for people who like to do it themselves
Free, practical and straight to the point. No accounts, no adverts in the way, no products pushed at you.
Shows the working
Every tool explains its formulas and includes a worked example, so you can see exactly where each number comes from.
Your figures, your answer
Use your own electricity price, room sizes and appliances. Metric and euro by default, with other units where it matters.
Honest about limits
Results are estimates to help you plan and compare. Each tool tells you when it’s worth getting a professional to check.
Not sure where to start?
Most people start with Electricity Cost Calculator: add the appliances you own and see what each one costs you a year.