If you’re building a real SaaS on top of WordPress Multisite, you eventually hit the same wall everyone hits:

How do you enforce plan limits reliably without breaking performance, risking data drift, or making the UX feel like a hack?

Most people duct-tape together a handful of actions, throw a few if checks into functions.php, and hope for the best.

We don’t do “hope for the best.”

At SampleHQ — a multi-tenant SaaS built fully on WordPress Multisite — we built a proper, predictable, enforceable limit system:
storage quotas, user limits, sample limits, image optimization, and bulk import throttling.

Here’s the full breakdown of how it works under the hood.

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1. The Source of Truth: plan-restrictions.php

Every rule, every limit, every cap lives in one place:

/functions/plan-restrictions.php

It’s the brain of the entire system.

Key Functions

• sf_get_site_plan()
  Returns 'light' or 'pro'. Defaults to 'light' if someone bypasses setup.
• sf_get_user_limit() / sf_get_sample_limit()
  Numbers for Light, 'unlimited' for Pro.
• sf_get_storage_limit()
  500MB for Light → 5GB for Pro (configurable).

This gives us something every SaaS needs:

One file to modify, test, and reason about
No scattered conditionals
No “magic rules” duplicated across plugins

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2. Real-Time Storage Usage (Not a Counter That Drifts)

Most platforms track usage with a database counter.

It works until it doesn’t.

One SFTP delete… one batch operation… one misfired plugin… and the counters drift.

We don’t rely on counters — we scan the tenant’s upload directory in real time:

function sf_get_current_storage_usage() {
    $upload_dir = wp_upload_dir();
    $upload_path = $upload_dir['basedir'];

    $total_size = 0;

    $iterator = new RecursiveIteratorIterator(
        new RecursiveDirectoryIterator($upload_path, RecursiveDirectoryIterator::SKIP_DOTS)
    );

    foreach ($iterator as $file) {
        if ($file->isFile()) {
            $total_size += $file->getSize();
        }
    }

    return $total_size;
}

Why this matters

• Accuracy: If the user deletes something, the quota reflects it immediately.
• No drift: No counters to reset or repair.
• Fast: PHP’s RecursiveIteratorIterator is memory-efficient and surprisingly fast.

This is the part where developers usually comment:
“Wait… WordPress can do that?”

Yes. It can. It just usually doesn’t.

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3. Automatic Image Optimization (The Secret Weapon)

A single unoptimized 10MB JPEG can eat 2% of a Light plan’s storage.

So every image upload goes through:

sf_optimize_uploaded_image()

We resize and compress immediately after WordPress creates the attachment:

imagejpeg($resized, $file_path, $quality);

Why this matters

• A 5MB upload → 150-200KB after optimization
• Reduces quota usage by up to 96%
• Prevents storage abuse without the user even noticing
• Works across avatars, sample uploads, and imports

It’s invisible, automatic, and arguably one of the most important UX improvements in the platform.

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4. Role-Aware Limit Messaging (To Drive Upgrades)

If the Owner hits the limit → they see:

“You’ve reached your plan limit. Upgrade to Pro.”

If a Manager hits the limit → they see:

“You’ve reached your plan limit. Please contact the Owner.”

The function behind it:

sf_get_user_limit_message()

Why this matters

• Owners see upgrade CTAs
• Managers/employees don’t get frustrated
• The right person receives the right message
• Zero confusion, less support, more upgrades

This isn’t UI fluff — it’s revenue design.

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5. CSV Import Throttling (The Hardest Problem in Any SaaS)

Bulk imports are the #1 way users accidentally (or intentionally) bypass limits.

So we validate every row during CSV processing:

foreach ($rows as $row_index => $row) {
    if ($import_type === 'users' && !sf_can_create_user()) {
        $limit_reached = true;
    }

    if ($limit_reached) {
        $results['failed'][] = [
            'error' => 'Plan limit reached...',
            'reason' => 'limit_reached'
        ];
        break;
    }

    // process normally
}

Why this matters

• No 10,000-row CSV loopholes
• No race conditions
• Limits apply exactly the same way as manual creation
• Predictable, testable behavior

This is the difference between “a plugin” and a platform.

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Final Thoughts

WordPress Multisite gives you an incredible foundation for building a SaaS — but only if you treat it like an engineering platform, not a blog CMS.

Limit enforcement is one of those areas where most SaaS products built on WordPress fall apart:

drift-prone counters
inconsistent rules
no messaging hierarchy
unoptimized uploads
loopholes through imports

SampleHQ solves this with:

• centralized plan logic
• real-time storage scanning
• automatic image optimization
• role-aware upgrade nudges
• bulletproof import throttling

If you want WordPress to feel like a real SaaS, this is the kind of engineering discipline that makes it possible.