The verdict in three sentences
On a 3G connection at ~400ms RTT, a heavy payment page (2.5 MB, LCP at 8s) loses customers before the pay button even appears. Each added second costs about 7% conversion, and 35 to 50% of West African traffic stays on 3G. The 2026 target: < 500 KB, LCP < 2.5s and INP < 200ms on the checkout page.
Heavy page vs optimized page
The difference does not show on office wifi; it shows on the phone of a customer in Kaolack at peak hour.
| Criterion | Heavy checkout | Optimized checkout |
|---|---|---|
| Total weight | 2.5 MB | < 500 KB |
| LCP on 3G | ~8s | < 2.5s |
| LCP on 4G | ~2.5s | < 1s |
| INP | > 400ms | < 200ms |
| Network requests | 40+ | < 15 |
| Third-party scripts | many | minimal |
Weight step by step
A checkout breaks into screens; each must stay light, especially the payment screen.
| Step | Typical unoptimized weight | Optimized target |
|---|---|---|
| Cart | 900 KB | 200 KB |
| Address / shipping | 600 KB | 120 KB |
| Payment screen | 1,000 KB | 180 KB |
| Confirmation | 400 KB | 80 KB |
| Analytics/third-party scripts | 500 KB+ | deferred |
PSP redirect vs inline SDK
The payment integration choice weighs on latency. A redirect to an external PSP page adds a full network round trip; a well-optimized inline SDK keeps the customer on your page but must stay light.
1. Performance budget. Set a hard ceiling: the payment page never exceeds 500 KB. Every new script must "earn its ticket".
2. Deferred loading. Analytics, chat, pixels: loaded after interaction, never before the pay button.
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3. Images and fonts. Modern formats (WebP/AVIF), system fonts or subsets; a single heavy custom font can add 1s to LCP on its own.
4. Measure on real 3G. Test with 3G throttling (400ms RTT, ~400 Kb/s), not fiber. Target LCP < 2.5s and INP < 200ms.
Mini case study
Moussa runs a meal delivery site in Thies, 3,000 checkouts/month, average basket 8,500 FCFA. His payment screen weighed 2.3 MB (LCP ~7s on 3G). Dropping under 500 KB (LCP ~2.3s), he gains ~4.5s. At ~7% conversion lost per second, the recovery potential is large: even a cautious +8 point checkout conversion gain on 40% of 3G traffic yields ~96 orders/month x 8,500 = 816,000 FCFA/month additional revenue, for about 3 days of optimization.
FAQ
How much does one second of latency cost? An order of magnitude of about 7% conversion lost per second added on the payment page.
What share of AOF traffic is on 3G? An estimate of 35 to 50% depending on country and area, with peaks in outskirts and rush hours. It cannot be ignored.
What weight should the payment screen target? Under 500 KB total, third-party scripts deferred, to hold an LCP < 2.5s on 3G.
PSP redirect or inline SDK? The inline SDK keeps the customer on your page but must stay light; the redirect adds a full network round trip. Choose by performance budget.
What Core Web Vitals targets? LCP < 2.5s and INP < 200ms on mobile, measured with real 3G throttling, not fiber.
Let's talk about your project. We optimize your checkout for African 3G and target green Core Web Vitals. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
