Coverage is the area divided by 1,000 sq ft. Product and finished spray each scale with that coverage — product by the label rate, finished spray by your carrier rate. The two are computed separately and never summed.

coverage_units   = area_sqft / 1,000

A. Product (concentrate)
   rate_per_1000  = per-acre ? rate_per_acre / 43.56 : rate_per_1000
   product        = coverage_units × rate_per_1000

B. Finished spray (carrier water)
   carrier_per_1000 = per-acre ? carrier_per_acre / 43.56 : carrier_per_1000
   finished_gallons = coverage_units × carrier_per_1000

C. Tank loads (carrier mode)
   tank_loads       = ceil(finished_gallons / tank_gal)
   product_per_tank = rate_per_1000 × (tank_gal / carrier_per_1000)
   last (partial) tank = total product − product_per_tank × (loads − 1)

Worked example: 4,800 sq ft at 3 fl oz / 1,000 sq ft, a 2 gal / 1,000 carrier, and a 4-gal tank → coverage 4.80; measure 14.4 fl oz (≈ 86 tsp); mix 9.6 gal finished spray; 3 tank loads (4 + 4 + 1.6 gal) at 6 fl oz per full tank, 2.4 fl oz in the final partial load.

Per-acre rates normalize to per-1,000 sq ft using 1 acre = 43,560 sq ft. Tank loads use ceil — a 2.4-load job is 3 fills, not 2 — and the last tank carries the remainder so the per-tank rows add back to the total. The defaults are an illustrative example, not a recommended rate for any product; your EPA label is the binding instruction.

Sources: Pesticide Environmental Stewardship (4,800 / 1,000 × 3 oz = 14.4 oz; 1 acre = 43,560 sq ft); DIY Pest Control (per-1,000-sq-ft method, carrier example); SprayCalc Pro (1–5 gal/1,000 backpack range, multi-unit output).