写这个内容之前先搜索了一下（要成为一种习惯）。发现一个帖子：

https://www.cpsenglish.com/question/4609

龙楠网友给出了解答。我想把这个foot表示“英尺”的问题再引申一下，尽量说清楚。

随便翻一本词典，都能查到在foot表示“英尺”这个意义的时候，其复数有两种形式：foot和feet。要留意！

以下的例句都是正确的：

six foot/feet tall

six foot/feet long

例子很多，不多说。

如果有连字符而充当形容词功能时，要用单数foot：

a four-foot-deep hole

a four-foot deep hole

a six-foot-tall man

a six-foot tall man

这些都是当代英语的习惯，大家也熟知。因此以前那些表示方法，如：

five-months-old, five-feet-long，two-thousand-feet-high等都是不规范的用法。我在徐广联的书中还看到有这些用法，需要更新了。

还有一个说法，我提一下：

Note that you always use foot as the plural in front of another noun. For example, if a gap is twenty feet wide, you refer to it as a 'twenty foot gap'. You do not refer to it as a 'twenty feet gap’.

a forty foot wall

(Collins Cobuild English Usage第二版，第四版）

这个用法是正确的，但是这里的foot是单数形式，不是复数形式（上面的说法不对，证据见Collins Cobuild English Grammar 4th的2.255节，可以对比看看），相当于是名词修饰名词，当然用单数，这个用法已不多见，最多的还是用连字符充当形容词的功能，这就好理解了：

a forty-foot wall

It's a twenty-five foot drop from this cliff.(Longman Dictionary of American English by Pearson Longman4th)

新概念2019版第3册P30:

......to the fifteen-foot wall which surrounded the president’s palace.

以前早的版本却是这样的：

......to the fifteen foot wall which surrounded the president’s palace.

我主要想说说foot（英尺）接inches（英寸）的时候的用法：

Wood博士在1959年回答一位读者关于此问题的时候这样解释道：

One has the impression (and it is borne out by Jespersen's quotations) that in modem times foot is more frequent when it is followed by a number indicating inches but the word inch(es) is not itself used: thus five feet, or five feet eight inches, but five foot eight.

就是说如果不接inches，要用foot，如：five foot eight。

如果接有inches（feet前面数字大于1），要用feet，如five feet eight inches。

Sylvia Chalker在English Grammar Word by Word中也说：

When we give the inches too, we say:

She’s five foot seven (NOT *five feet . . .)

在Collins Cobuild English Usage第二版2004中也有：

If you are expressing size using feet and inches, you do not have to say 'inches'. For example, you can say that something is two foot six long. However, you do not say 'two feet six’ or 'two foot six inches.'

He's Italian, and immensely tall, six feet six inches.

但是同样是这本书，又提到：如果inches后面有tall，high或long时，可以用复数形式的foot：

She's five foot eight inches tall.

这个句子是正确的。

这些说法中除了最后一个说法其他都不太符合当代英语的使用情况。

同样是Wood博士，他在其1981年的著作“Current English Usage修订版”中提到：

He is six foot four. = He is six feet four.

后面没有inches，用foot和feet都可以，但要注意确实用foot比用feet的多。有很多资料支撑这种说法：

six foot three = six feet three（Zandvoort）

He's six foot eight (or six feet eight or six feet eight inches).(A Communicative Grammar of English 3rd by Geoffrey N. Leech)

但如果后面有inches，foot前面的数字大于1，此时用feet的情况多过用foot（注意这里的foot是复数形式的foot）。只举foot的例子，用feet的更多：

six feet/foot two inches （Eastwood）

She's five foot eight inches tall.（Collins Cobuild English Usage第二版2004）

用“Good Word Guide-The fast way to correct English2010年第六版”上的一个说法作总结：

For measurements in feet and inches, feet is preferred in more formal and precise contexts:

seven feet four inches

In informal usage the word inches is omitted and the plural form foot is more frequent: seven foot four.

In such expressions as three feet high or ten foot wide, the same distinctions of formality and precision may be applied:

The wall must be exactly three feet high.

The room is about ten foot wide.

For larger measurements, such as the height of a mountain, feet is preferred in all contexts.

用中文做个总结：

1.后面不接或者说省略inches，用foot和feet都是正确的，只是用foot比用feet要普遍。

2．接inches（foot前的数字大于1），分两种情况，一是inches后面有tall，high或long等词时，foot和feet都是正确的，且使用feet更加普遍；二是inches位于句尾，此时要用feet，几乎不用foot。

用实例说明如下：

He is six foot/feet four.           （都对，但用foot要更为普遍）

She's five feet/foot eight inches tall.   （都对，但用feet要更为普遍）

He's six feet eight inches.        (正确，这里的feet不宜改为foot)