WATFUL

Make every watt count.

Practical power and energy calculators with transparent formulas, editable assumptions and shareable results.

Calculators

How long a battery actually powers your load — after depth of discharge and inverter losses.

Convert between amp-hours and watt-hours at any nominal voltage — the first step of every battery calculation.

How many peak sun hours and days your panels need to refill a battery, after system losses.

How big a bank your daily consumption needs, sized for days of autonomy and usable depth of discharge.

The continuous and surge rating your loads need, plus the battery-side current to plan cabling for.

How much voltage your cable run loses — and the cross-section that keeps it inside the 3% guideline.

What an appliance actually costs to run per day, month and year, at your electricity price.

What a heat pump saves against direct electric heating — from heat demand, SCOP and your electricity price.

American Wire Gauge to metric cross-sections and back, with the safe next-size-up substitute.

Running and starting watts your loads need, and the common generator size that covers both.

Fuel burn at the load you actually run — fitted from your datasheet's figures, not just the full-load spec.

How long you need to drive to refill your house battery — and how much current that pulls from the alternator.