Rainy weekend: size as if solar = 0

The calculator assumes no recharge. That is the correct rain/canopy case. Do not credit panel watts you will not harvest.

12V DC vs AC: The 1,619 Wh worked example uses the AC inverter path (η=0.90) because this mixed camping load includes laptop/lights through the inverter — same as the homepage sample. If the fridge is on the station’s 12V port, do not apply η=0.90 to that 12V energy. Set Inverter efficiency = 1.00 for a DC-only fridge path. See cooler vs fridge.
WattNeeds defaults (AC path): inverter efficiency η=0.90, DoD=0.90, buffer=0.15. One-liner: nameplateWh = (whPerDay × days × 1.15) / (0.90 × 0.90). Always re-check continuous watts and surge against the station inverter.
Example sizing for a 12-hour outage: mini fridge 40 watts times 12 hours is 480 Wh, laptop 180 Wh, LED 50 Wh, phone 20 Wh, total 730 Wh. A 15 percent buffer makes 839.5 Wh. Divided by 0.90 depth of discharge and 0.90 inverter efficiency, the AC nameplate is about 1,036 Wh, which fits the about 1,000 Wh class (results 513 to 1,152). Compare that result to the station label. All 12 V DC devices would be about 933 Wh. The fridge 40 W is an average because the compressor cycles.
EXAMPLE. 480 + 180 + 50 + 20 = 730 Wh. 730 × 1.15 = 839.5. 839.5 / 0.90 / 0.90 = 1,036.42, shown as ~1,036 Wh. 12 V DC skips the inverter: 839.5 / 0.90 = 932.78, shown as ~933 Wh. Fridge 40 W is an average over the window.
Camping sample: fridge band 320, laptop 140, lights 50, phones 60, total 570 Wh per day. One day AC nameplate is about 809 Wh. Two days with solar at zero: 1,140, then about 1,267, about 1,457, and about 1,619 Wh. The 1,267 and 1,457 steps are rounded. A 1,000 Wh label delivers 810 Wh, about 1.4 days, short of two wet days. A 2,000 Wh label delivers 1,620 Wh, about 2.8 days. If the fridge is on 12 V DC, run it as a separate pass at efficiency 1.00 and keep the AC loads at 0.90.
EXAMPLE. 570 × 2 = 1,140. 1,140 ÷ 0.90 ≈ 1,267. 1,267 × 1.15 ≈ 1,457. 1,457 ÷ 0.90 ≈ 1,619 Wh with solar = 0. 320 Wh/day planning band is not the CFX3 282 test point. EcoFlow camping guide.
Example: a 1,000 Wh station label times 0.90 inverter efficiency times 0.90 depth of discharge equals 810 Wh usable on AC. A continuous 100 W AC load runs 8.1 hours, about 8 hours. Plan on about 81 percent of the label for AC.
EXAMPLE. 1,000 × 0.90 × 0.90 = 810 Wh usable AC. 810 / 100 W = 8.1 hours. Plan on ~81% of the label for AC.

Worked load (homepage camping sample)

320 Wh/day fridge planning band ≠ CFX3 282 Wh/day manufacturer test point. The fridge row is the homepage camping sample (mild-condition planning band). It is not the Dometic CFX3 35 spec of 0.98 Ah/h × 12 V × 24 h = 282 Wh/day (Dometic draw method). Nameplates below use the AC default (η=0.90).

DeviceCountWh/day
Camp fridge (avg)320 Wh/day planning band (not CFX3 282 Wh/day)320
Laptop70 W × 2 h140
LED lights10 W × 5 h50
PhonesUSB Wh/day60
Total570 Wh/day

Two days, solar = 0:

  1. 570 × 2 = 1,140 Wh to loads
  2. 1,140 / 0.90 = 1,267 Wh battery draw (inverter)
  3. 1,267 × 1.15 = 1,457 Wh with buffer
  4. 1,457 / 0.90 = 1,619 Wh nameplate

nameplate = 570 × 2 × 1.15 / (0.90 × 0.90) ≈ 1,619 Wh

What a 1000 Wh vs 2000 Wh nameplate actually delivers

Delivered to loads at defaults ≈ nameplate × 0.90 × 0.90 = 81% (no extra buffer on the way down):

NameplateDelivered WhDays at 570 Wh/day
1,000 Wh8101.4 — short of two wet days
2,000 Wh1,6202.8 — covers this load

Lighter 500 Wh/day camp (skip laptop, milder fridge): 500 × 2 × 1.15 / 0.81 ≈ 1,420 Wh nameplate. Still above 1 kWh if you want two dark days.

Bluetti’s public method is watts × hours, then divide by ~0.85 for conversion (Bluetti size guide). Jackery splits capacity (Wh) from output (W) (Jackery buying advice) and publishes a lumped runtime factor of capacity × 0.8 ÷ watts (Jackery FAQ). WattNeeds keeps η, DoD, and buffer as separate knobs (AC default 0.90 × 0.90 = 0.81 delivered, before the 1.15 buffer on the way up).

Wh calculator — set days = 2, leave solar out. Solar vs battery · Weekend camping

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