An inverter needs to support both the appliances running together and the extra demand when equipment starts. Add each appliance’s running watts, quantity and startup data, then compare the continuous and surge estimates separately.
Formula and assumptions: total running load = sum(running watts × quantity). Continuous capacity estimate = running load × (1 + selected headroom). The default one-start scenario adds the largest single-unit startup increment to all running loads. The all-start scenario sums each unit’s startup watts. Direct startup watts means the whole unit’s startup demand, not extra watts above running consumption.
Household example: a 150W refrigerator with an illustrative 900W startup demand and two 60W fans total 270W running load. At 25% headroom, the continuous estimate is 337.5W. With the fans running as the refrigerator starts, estimated demand is 1,020W. A 1kW continuous nameplate option therefore does not by itself prove the inverter can supply startup demand: its documented surge watts/VA, duration and other manufacturer limits must be checked.