以下详细说明暂以英文提供。
How much paint does a room actually need?
One gallon of interior paint covers roughly 350–400 square feet of smooth, primed wall in ideal conditions. Textured surfaces, fresh drywall that has never been sealed, and big color changes all pull that number down, which is why the calculator lets you set the coverage yourself. When in doubt, plan on the lower figure — a half-used gallon on the shelf beats a second trip to the store with a roller still wet.
Why openings and coats change the math
Doors and windows are subtracted first because nobody paints glass — the standard approximations of 21 ft² per door and 15 ft² per window are close enough for ordering. Coats matter just as much: two coats is the norm for even color and a washable finish, and the calculator doubles the paintable area before dividing by coverage. For a dramatic dark over light walls, a tinted primer usually costs less than a third coat.
中国本地参考
日常计算时值得知道的中国本地规则：
- 计量的单位习惯: 住房面积用平方米，土地常用亩（1 亩 ≈ 666.7 平方米）；里程用公里，油耗用 L/100km。
- 日期与数字格式: 日期写作 2026年10月13日（年-月-日）；大数习惯用万、亿（1 万 = 10,000，1 亿 = 100,000,000）。
- 法定节假日: 全年法定节假日 11 天，春节与国庆为长假；调休安排每年由国务院办公厅发布。
- 速度与限速: 高速公路最高限速 120 km/h，城市快速路多为 80 km/h，均以公里每小时计。
- 鞋服尺码: 鞋码用中国码（毫米制），服装常用 155/80A 这类身高围度组合，与欧美码不同。
数据核对：2026 年 10 月
常见问题
Does this include the ceiling?
No — the calculation covers walls only. For a ceiling, measure the floor area instead (they match in most rooms), and count on flat ceiling paint at the same coverage figure.
What coverage should I enter?
Keep 350 ft² per gallon for typical interior latex on primed walls. Drop to about 300 for heavy texture or bare drywall, and check the can — manufacturers print tested coverage that is usually in the 250–400 range.
How do the suggested can sizes work?
Gallons are rounded up to a whole number, then broken into 5-gallon buckets plus 1-gallon cans. Six gallons comes back as one 5-gallon bucket and one single gallon, which is usually cheaper than seven singles.