TOOLS & CALCULATORS
Work it out before you buy.
Free, instant planning calculators for power, water and household preparedness. No sign-up, no app - the working is on the page with every result.
ENERGY & SOLAR
Power Station Runtime Calculator
Estimate real backup hours from usable capacity, average load and inverter losses.
1,000 Wh − 15% ÷ 65 W ≈ 13 h
Open calculatorWATER INDEPENDENCE
Emergency Water Storage Calculator
How many litres your household actually needs for a given number of days.
4 people × 7 days × 4 L → 112 L
Open calculatorENERGY & SOLAR
Solar Recharge Calculator
How long a panel really takes to refill a battery, after weather and angle losses.
800 Wh ÷ (200 W × 75%) ≈ 5.3 h of strong sun
Open calculatorEMERGENCY PREPAREDNESS
Emergency Kit Builder
Turn household size and days of cover into an exact supplies list with quantities.
4 people · 3 days → 48 L water, 36 meals
Open calculatorENERGY & SOLAR
What Size Power Station Do I Need?
Turn a list of appliances and blackout hours into a starting capacity to shop against.
1,840 Wh/day × 1 day ÷ 0.85 ÷ 0.8 ≈ 2,710 Wh
Open calculatorWATER INDEPENDENCE
Rainwater Collection Calculator
Estimate yearly harvest from your roof and rainfall, and the tank size a dry spell forces.
60 m² × 800 mm × 80% ≈ 38,400 L/year
Open calculatorENERGY & SOLAR
Appliance Wattage and Energy Use Library
Turn any appliance's average draw into yearly kilowatt-hours and cost, with a library of typical figures.
100 W x 6 h x 7 d/wk ≈ 219 kWh/yr
Open calculatorEMERGENCY PREPAREDNESS
Blackout Backup Planner
Test whether your battery and solar can cover a planned outage, and what to shed if they can't.
850 Wh usable ÷ 92 W ≈ 9.2 h runway against a 24 h outage
Open calculatorENERGY & SOLAR
Off-Grid Power Cost Estimator
Estimate a system's true cost per kWh over its life, and how that compares with staying grid-tied.
4,000 upfront + 2% upkeep ÷ (1,800 kWh × 15 yr) ≈ 0.19 per kWh
Open calculatorWATER INDEPENDENCE
Water Container Planner
Turn a litres target into a mixed list of drums, jerrycans and bottles you can actually buy and store.
240 L → 1 × 200 L drum + 2 × 19 L bottles + 1 × 10 L jerrycan (3 containers)
Open calculatorWATER INDEPENDENCE
Rainwater Tank Sizing Calculator
Size the purchase tank from your dry-spell demand and the rain that falls inside the dry spell, not from a rule of thumb.
3,150 L demand − 1,200 L in-spell rain, plus 20% headroom → a 2,500 L tank
Open calculatorWATER INDEPENDENCE
Water Pump Sizing Estimator
Turn lift, pipe run and daily volume into the head, flow and power a pump actually has to deliver before you buy one.
2,000 L in 4 h at 18.9 m head ≈ 86 W motor input, 343 Wh/day
Open calculatorWATER INDEPENDENCE
Water Filter Replacement Tracker
Find out when a filter cartridge truly expires: the earlier of its litre capacity or its calendar life, measured from the day you fitted it.
Capacity would last 250 days but the 6-month clock ends first: due in 82 days
Open calculatorWATER INDEPENDENCE
Water Storage Rotation Planner
Build a drink-then-refill rhythm for stored water so nothing expires in the container, and nothing stale survives in the cupboard.
200 L at 12 L/day empties in 17 days, far before the 6-month best-before: refill next month
Open calculatorFOOD & GARDENING
Garden Irrigation Water Calculator
Work out the litres your beds really need each week after rain, what a dry spell costs in water, and how long the line must run.
20 m² × 15 mm net ÷ 90% efficiency ≈ 333 L/week, 5.6 h on a 60 L/h line
Open calculatorENERGY & SOLAR
Can It Run This Appliance? Checker
Test any appliance against a power station's continuous rating, surge rating and stored energy before you discover it at the socket.
120 W run with a 700 W surge against a 600/1,200 W station: Yes, ~7.1 h runway
Open calculatorENERGY & SOLAR
Battery Capacity Converter
Move between volts, amp-hours and watt-hours, and see what any pack really gives you at a chosen load.
12 V × 100 Ah = 1,200 Wh; an 80 W load runs ~12 h usable, about 10 h after losses
Open calculatorENERGY & SOLAR
Portable Solar Panel Matcher
Find the panel wattage that replaces a power station as fast as you use it, and see whether the one in your cart actually keeps up.
Replacing 500 Wh/day over 4 sun hours at 75%: needs a ~170 W panel; a 100 W panel covers ~300 Wh
Open calculatorENERGY & SOLAR
Appliance Running Cost Calculator
Compare what an old appliance costs to run against an efficient replacement, and see how many years the upgrade takes to pay for itself.
A 150 W unit run 8 h/day vs a 60 W replacement at 0.30/kWh: saves ~79 a year, pays back a 200 upgrade in ~2.5 years
Open calculatorENERGY & SOLAR
Power Bank Flight-Capacity Checker
Convert a power bank's milliamp-hours to watt-hours and get a straight verdict against the airline carry-on limits before you reach the gate.
20,000 mAh at 3.7 V = 74 Wh: under 100 Wh, allowed in the cabin with no approval
Open calculatorEMERGENCY PREPAREDNESS
Battery and Torch Planner
Size the batteries and power you need to keep the lights on through a night or a multi-day outage, from torches and lanterns you actually own.
5 lit hours a night on an 8 W lantern for 3 nights needs 120 Wh; a 300 Wh bank with a 20% reserve covers it with room
Open calculatorEMERGENCY PREPAREDNESS
72-Hour Preparedness Kit Checker
Score the supplies you already own against the seventy-two-hour standard for your household, and see exactly which category leaves you short.
Family of four with 30 L water and 24 meals: 82% kit-ready, water at 2.5 days, no radio the weak point
Open calculatorEMERGENCY PREPAREDNESS
Household Outage Planner Tool
Turn a planned outage length into one honest shopping list: water, ready meals, lighting energy and daily rhythm for the whole household.
Four people, five days: 80 L water, 60 ready-to-eat meals, 150 Wh of lighting energy to stock for
Open calculatorEMERGENCY PREPAREDNESS
Emergency Food Quantity Calculator
Convert people and days into the real food numbers: total calories, meal counts, approximate stocking weight, cooking water and cost.
Four people for seven days: 61,600 kcal, 84 meals, roughly 17 kg of dry staple weight, 42 L cooking water
Open calculatorEMERGENCY PREPAREDNESS
Car Emergency Kit Builder
Size a boot kit for your car, your climate and your worst realistic stranding: water, food, warmth and the fixed safety items.
Two people, a 12-hour stranding with one freezing night: 3 L of water (6 bottles), 8 food units, 4 warm layers
Open calculatorEMERGENCY PREPAREDNESS
Preparedness Gap Assessment
Rate seven preparedness domains from nothing to robust, and get one readiness score plus the specific gap that should be fixed first.
Ratings of 1, 2, 1, 2, 1, 0 and 1 across the seven domains score 38% ready, with comms and drill the clear first fix
Open calculatorEMERGENCY PREPAREDNESS
Emergency Gear Budget Planner
Phase a preparedness budget in the right buying order and see exactly how far your money reaches before the next gap needs next month.
A 500 budget for four: kit phase 240, water 80, power 150 all covered, first aid and comms phase short by 30
Open calculatorFOOD & GARDENING
Raised Garden Bed Calculator
Size your raised beds honestly: soil volume to buy, bag counts and cost, reachable width, and the yearly top-up that keeps them productive.
A 3 × 1.2 m bed at 25 cm deep needs 0.9 cubic metres: about 900 litres, eighteen 50-litre bags
Open calculatorFOOD & GARDENING
Seed Quantity and Plant Spacing Planner
Turn bed area and crop spacing into plant counts, then into the seeds to sow after germination odds and succession rounds.
3.6 square metres at 30 cm spacing: about 40 plants, roughly 47 seeds sown at 85% germination
Open calculatorFOOD & GARDENING
Compost Volume Calculator
Size a compost bin to your real waste: raw volume, the brown-material balance, how fast it fills, and how much finished compost to expect.
A 1 × 0.8 × 0.8 m bin holds about 640 litres; 40 L of greens plus 80 L of browns weekly fills it in roughly five weeks
Open calculatorFOOD & GARDENING
Food Dehydrator Batch Planner
Turn fresh weight into dried weight, jar counts and tray loads: know how many runs a harvest needs and what it will fill before you slice anything.
4 kg of apricots drying to 15 percent weight gives 600 g: two full 250 g jars with a part-jar left over, in two tray loads
Open calculatorFOOD & GARDENING
Food Storage Container Planner
Size dry-food storage to real use: how many weeks your stock covers, the container pack that holds it, and the rotation date the shelf earns.
48 L of stored grain at 4 L weekly use covers twelve weeks, packs into nine 5 L bins plus three 1 L jars, and the oldest bin is due for rotation review at month six
Open calculatorFOOD & GARDENING
Harvest Preservation Planner
Split a glut three ways before it rots: fresh eating weeks, freezer kilos and jar counts for canning or drying, sized to how the household really eats.
20 kg of tomatoes at 2.5 kg weekly eating gives eight kilos fresh, seven frozen and five jarred: about ten 0.5 kg jars and just over three weeks of fresh gluts
Open calculatorENERGY & SOLAR
Home Energy Savings Calculator
Test an energy upgrade before you buy: annual saving, payback years, the ten-year net with rising tariffs, and the break-even the invoice has to beat.
An 18 percent cut to a 1,200 annual bill saves 216 in year one, pays back a 600 investment in under three years, and nets about 2,000 over a decade as tariffs rise
Open calculatorEQUIPMENT & MAINTENANCE
Reusable vs Disposable Cost Calculator
Settle the buy-once debate with maths: break-even time, lifetime saving and the true annual cost of reusable versus disposable, care included.
A 60 reusable item costing 5 a year to care for beats 40 a year of disposables: break-even inside two years and about 115 saved across a five-year life
Open calculatorFOOD & GARDENING
Compost Tumbler vs Worm Farm Matcher
Pick the composter that fits your waste and space: worm farm, tumbler or hot bin, matched by weekly volume, footprint and how much is kitchen scraps.
Twenty weekly litres that is mostly food scraps in one square metre points to a worm farm: roughly eighty-five litres a month processed indoors, under half a square metre, ending as castings
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The calculator library grows with every guide we publish - rainwater yield, soil volume, inverter sizing and more are on the way. The planning method behind each tool is documented on its page, so you can always check the working.
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