Introduction
This case study is a hypothetical, illustrative scenario — invented numbers walking through the real method, so you can see how a multi-room estimate comes together. It is not a report of actual work performed.
The scenario: a family repainting the main living areas of a 3-bedroom apartment before moving in — living room, two bedrooms, hallway, and all the trim — with mid-range paint, two coats throughout, and previously painted walls in decent shape. Watch how the estimate builds room by room, where the judgment calls land, and what the final shopping list looks like.
Follow along with your own dimensions in the Interior Paint Calculator; the method is documented in the complete guide.
The Project
| Room | Dimensions | Openings | Surfaces |
|---|---|---|---|
| Living room | 16 × 20 ft, 9 ft ceilings | 2 doors, 3 windows | Walls (eggshell), ceiling (flat), trim (semi-gloss) |
| Bedroom 1 | 12 × 15 ft, 8 ft ceilings | 1 door, 2 windows | Walls (eggshell), ceiling (flat), trim |
| Bedroom 2 | 11 × 13 ft, 8 ft ceilings | 1 door, 1 window | Walls (eggshell), ceiling (flat), trim |
| Hallway | 4 × 18 ft, 8 ft ceilings | 4 doors, 0 windows | Walls (satin — high traffic), ceiling (flat), trim |
Walls are previously painted latex in decent shape — no primer needed. Coverage: 350 sq ft per gallon. Waste: 10%. Two coats everywhere.
Room-by-Room Math
Living room
Walls: 2 × (16 + 20) × 9 = 648 sq ft; openings = (2 × 21) + (3 × 15) = 87; net = 561 sq ft. Two coats = 1,122 sq ft ÷ 350 = 3.206 gal × 1.10 = 3.53 → 4 gallons eggshell.
Ceiling: 16 × 20 = 320; two coats = 640 ÷ 350 = 1.83 × 1.10 = 2.01 → 2 gallons flat (rounds up from just over 2 — the round-up policy at work).
Bedroom 1
Walls: 2 × (12 + 15) × 8 = 432; openings = 21 + 30 = 51; net = 381 sq ft. Two coats = 762 ÷ 350 = 2.18 × 1.10 = 2.39 → 3 gallons.
Ceiling: 12 × 15 = 180; two coats = 360 ÷ 350 = 1.03 × 1.10 = 1.13 → 2 gallons.
Bedroom 2
Walls: 2 × (11 + 13) × 8 = 384; openings = 21 + 15 = 36; net = 348 sq ft. Two coats = 696 ÷ 350 = 1.99 × 1.10 = 2.19 → 3 gallons.
Ceiling: 11 × 13 = 143; two coats = 286 ÷ 350 = 0.82 × 1.10 = 0.90 → 1 gallon.
Hallway
Walls: 2 × (4 + 18) × 8 = 352; openings = 4 × 21 = 84; net = 268 sq ft. Two coats = 536 ÷ 350 = 1.53 × 1.10 = 1.68 → 2 gallons satin.
Ceiling: 4 × 18 = 72; two coats = 144 ÷ 350 = 0.41 × 1.10 = 0.45 → 1 gallon.
The Trim Calculation
Linear feet of baseboard + casings: living room 72 + (2×20) + (3×15) = 157; bedroom 1: 54 + 20 + 30 = 104; bedroom 2: 48 + 20 + 15 = 83; hallway: 44 + (4×20) = 124. Total ≈ 468 linear feet. Two coats = 936 ÷ 175 (midpoint of the 150–200 rule) = 5.35 → 6 quarts semi-gloss (1.5 gallons equivalent — buy quarts, not gallons, for color flexibility). Doors: 8 doors × ~1 quart per 2–3 doors per coat ≈ 3 quarts per coat × 2 coats = 6 quarts, but doors share the trim paint — the 6-quart trim total covers typical doors if they’re the same semi-gloss; add 2 quarts if doors are a separate color. The trim math is derived in the formula guide.
The Shopping List and Budget
| Item | Quantity | Unit price | Subtotal |
|---|---|---|---|
| Wall paint, eggshell (living + bedrooms) | 10 gal | $50 | $500 |
| Wall paint, satin (hallway) | 2 gal | $52 | $104 |
| Ceiling paint, flat | 6 gal | $30 | $180 |
| Trim paint, semi-gloss | 6 qt | $16 | $96 |
| Supplies (tape, covers, brushes, cloths, trays) | — | — | $150 |
| Total DIY | $1,030 |
Professional quotes for this scope (hypothetically) would land around $3,000–4,500 — the DIY saving is roughly two-thirds, per the DIY vs pro comparison. The family in this scenario chose DIY for the bedrooms and hallway and hired a pro for the 9-ft living room ceiling and trim — the hybrid path.
What the Scenario Teaches
- Small rooms are wall-heavy: the hallway’s 268 sq ft of wall from a 72 sq ft floor shows why per-room rules of thumb beat per-square-foot-of-floor guessing.
- Ceilings add up: 6 gallons of ceiling paint is the line item most first-time estimators forget entirely.
- Sheen splits the order: three wall products (eggshell, satin, flat ceiling) plus trim — four line items, each estimated separately, exactly as the material guide recommends.
- The round-up compounds across rooms: bedroom 2’s ceiling at 0.90 → 1 gallon and the living room ceiling at 2.01 → 2 gallons show the policy working as designed — small surpluses, never shortfalls.
- No primer line item because the walls were previously painted and sound — the judgment call the common mistakes guide warns about in reverse (priming when unneeded wastes money too).
Related Guides
- Complete Guide — the method this scenario demonstrates.
- Cost Guide — building budgets like this one.
- How to Estimate — measuring your own rooms.
- DIY vs Pro — the hybrid path this scenario chose.
- Project Checklist — executing a multi-room project in order.
Get Your Estimate
Your home has different dimensions, but the method is identical: measure each room, deduct openings, divide by coverage, round up. Run your own scenario through the Interior Paint Calculator and build a shopping list like the one above.
Disclaimer: This case study is hypothetical and illustrative; quantities and prices are worked examples, not quotes. Calculator results are planning estimates based on the dimensions and coverage rates you enter. Actual paint requirements vary with surface texture, porosity, color change, and application method. Always check the manufacturer’s data sheet for coverage, drying, and recoat times. Homes built before 1978 may contain lead paint — follow EPA RRP rules and local regulations for disturbance and disposal, and verify local VOC limits and paint-waste disposal rules before you start.
